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Archive for the ‘Male Genetics’ Category

Male Infertility – Genetics & IVF Institute

Among infertile couples, either partner may contribute to the failure to conceive. It is estimated that 30-40% of infertility is due to male abnormalities, another 20% to a combination of various factors, and about 30-40% to problems with the female partner.

The Genetics & IVF Institute offers expert diagnosis and treatment of male infertility. Our male infertility treatment offers the following benefits:

If donor sperm is needed, our on-site sperm bank, Fairfax Cryobank, provides a large selection of high quality, fully screened donor sperm. In fact, GIVF patients who choose donor sperm from Fairfax Cryobank can enjoy free shipping and handling, as well as same day delivery. Click here to learn more about Fairfax Cryobank.

An important component in the treatment of men with infertility is establishing the correct diagnosis. Our medical specialists conduct a thorough clinical evaluation of each couple. State of the art semen analysis and specialized sperm function testing are available, including measurement of sperm capacitation and acrosome reaction, computer assisted sperm motion analysis (CASA), sperm antibody, and leukocyte quantitation. An appropriate individualized treatment is then recommended.

Intracytoplasmic sperm injection (ICSI), is the direct injection of sperm into eggs obtained for in vitro fertilization (IVF). GIVF has extensive experience with ICSI and have established thousands of pregnancies using this technique. ICSI frequently permits the establishment of pregnancy in even the most difficult types of male infertility, including men who have fewer than 100 sperm in their semen. For men with no sperm at all in their semen, sperm can be obtained directly from the testis with non-surgical sperm aspiration (NSA). Testicular sperm can fertilize when injected directly into eggs using ICSI.

The ICSI Process:

ICSI has been widely used for over ten years. GIVF performed the first ICSI pregnancy in the US and since then the procedure has become the standard of care for male factor infertility. The American Society for Reproductive Medicine (ASRM) considers it a safe, effective procedure that has helped thousands of men becomes fathers. If you have questions or concerns about ICSI, please let your doctor or nurse know so that we can discuss it with you.

The difference between IVF and ICSI is in how the sperm meets the egg. With traditional IVF, the sperm is poured on the egg. That is to say that the sperm is put into the petri dish that the eggs are in and fertilization takes place in the dish the same way it would in the fallopian tubes. Millions of sperm compete to fertilize each egg.

With ICSI, an individual sperm is injected into a single egg. ICSI is used when there is a problem with the sperm; thereby the likelihood of fertilization is increased if we inject the sperm directly into the egg. ICSI does not guarantee that fertilization takes place, but it does ensure that sperm meets egg. With traditional IVF, the sperm may never pass through the outer zona of the egg. Your doctor will advise you if ICSI is recommended for you based on the results of the semen testing and a few other risk factors.

Non-surgical sperm aspiration (NSA) is a quick and painless procedure performed in our clinic under sedation. A tiny needle is used to extract sperm directly from the testis. While the ejaculate normally contains 100 million to 300 million sperm, aspiration of as few as 100-200 sperm by NSA have been enough to achieve pregnancy when it is combined with ICSI.

NSA may be recommended for men who:

It is possible to reverse a vasectomy by having bypass surgery, but the operation is frequently unsuccessful, especially for men with long-standing vasectomies. Additionally, sperm quality after vasectomy reversal is often reduced and ICSI is required even if sperm appear in the ejaculate. For many men, NSA eliminates the need for vasectomy reversal surgery.

Prior to the development of NSA, men with no sperm in their ejaculate had to undergo surgery to remove sperm either from their testes or from tubes connected to the testis. The operation required a costly hospital stay and a lengthy recuperation. NSA is a quick and painless procedure performed at GIVF, does not require hospitalization, and recovery is virtually immediate. It should be noted that for some men, a single NSA procedure may yield enough sperm to permit sperm freezing for several subsequent ICSI attempts.

NSA must be done with ICSI because testicular sperm cannot enter eggs by themselves. In order to accomplish this, the female partner receives a series of medications to increase the number of eggs created by the ovary as in a conventional IVF cycle. When the eggs grow to adequate size, they are extracted non-surgically at GIVF under sedation, and NSA is scheduled the same day. After egg retrieval and sperm aspiration, our embryologists inject each egg with a single sperm. Two days after the procedures, definite information regarding fertilization of the eggs, and the number of embryos are available. Embryos are transferred back to the uterus two or three days following fertilization; additional embryos may be cryopreserved (frozen), as requested.

If donor sperm is needed, our on-site sperm bank, Fairfax Cryobank, provides a large selection of high quality, fully screened donor sperm. In fact, GIVF patients who choose donor sperm from Fairfax Cryobank can enjoy free shipping and handling, as well as same day delivery. Click here to learn more about Fairfax Cryobank.

Click here or call 800.552.4363 or 703.698.7355 to schedule a fertility consultation at GIVF.

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Male Infertility - Genetics & IVF Institute

The Genetics of Balding | Understanding Genetics

Finding a gene can be like a treasure hunt.

At first it might seem weird that researchers found a bit of DNA involved in baldness but that they can't figure out why it is involved. The reason for this has to do with the way people find DNA involved in disease.

Human DNA is a long string of 3 billion letters (or bases). Each human is unique because these letters are arranged in a certain order*.

It is too expensive to figure out all of the bases of the DNA from the hundreds or thousands of people involved in a typical study. So what scientists have done is figured out millions of places in human DNA where these letters are often different between people. (This is called the HapMap.)

These differences or SNPs (single nucleotide polymorphisms) work like landmarks to help scientists find which part of the DNA to focus on. They are like clues on a treasure map.

The first part in using a treasure map is narrowing down what part of the world the treasure is in. Imagine the map shows that the treasure is in San Francisco. Then there might be clues that the treasure is near a certain hill or near an oddly shaped tree. Perhaps the treasure is buried near the tower on Mt. Sutro.

With this information, the treasure seekers can get digging. If they know a treasure is in San Francisco, they can't just dig up the whole city. But if they know it is near the tower on Mt. Sutro, then they can dig all over that area.

This is how DNA searches work too. Scientists use SNPs as landmarks to narrow down DNA regions to focus on.

Instead of a treasure map, scientists use the HapMap. They use this map to compare the DNA of people with and without the condition they are interested in. In these studies, scientists compared the DNA of balding and not balding men.

The first study looked at German men. One experiment in this study compared 296 balding men to 347 German men and women who were not seriously bald. The researchers looked at over 500,000 different spots on their DNA and found that bald people shared a number of landmarks in a 1.7 million base chunk of chromosome 20. They had narrowed it down to San Francisco.

More clues led them to a single letter difference that was shared by many of the balding men. A second experiment looked at 319 bald men and compared them to 234 men who weren't bald by the age of 60. This second experiment confirmed the results of the first one.

The second study was done similarly. They compared 578 Swiss men with male pattern baldness to 547 Swiss men who weren't balding. They found a different SNP near the one the first study found. They confirmed that this DNA difference as associated with baldness in over 3000 other individuals from a variety of Northern European countries.

So these two studies have narrowed down where the "treasure" is. They made it to Mt. Sutro. They know that something on a small section of chromosome 20 is partly responsible for balding in Northern European men.

The next steps will be to do some serious digging and to find the treasure. In other words, the researchers need to figure out what in this region is causing these men to bald early. And once they do that, they need to find out why these men go bald. With that information, they might be able to create medicines that can treat baldness.

Usually there is a gene nearby that researchers can investigate. In this case, there isn't. The SNPs are in the middle of nowhere with the nearest gene being at least 350,000 bases away. So researchers have their work cut out for them.

In doing these studies, the researchers also rediscovered the DNA difference that men can inherit from their mom's dad that can lead to early balding.

*The exception is identical twins who have essentially the same DNA but are still unique for environmental reasons.

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The Genetics of Balding | Understanding Genetics

Genetics / Does the male or female carrier the gene for twins.

Expert: Kristiann Dougherty, PhD - 9/22/2007

I can answer questions related to Mendelian inheritance, heredity, population genetics, genetic diseases, molecular biology techniques, transcription/translation, mitosis, meiosis. Please don't ask for predictions about what (or whom) your unborn baby will look like. I can't see the future, and in most cases, I am unable to provide a satisfactory answer, just a range of possiblities. That being said, I will attempt to answer questions related to children already born.

Conducted research in the field for about 12 years. Also am a Biology professor so I teach most of these subjects on a regular basis. Familiar with many examples to use as illustations.

Organizations Natl Association of Biology Teachers

Publications Journal Biological Chemistry Proceedings of the National Academy of Science (PNAS) Cancer Research

Education/Credentials BS in Biology, with concentration in Genetics - Purdue University PhD in Molecular Biology and Human Genetics - Johns Hopkins University

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Genetics / Does the male or female carrier the gene for twins.

Genetics – NHS Choices


Genetics is the branch of science that deals with how you inherit physical and behavioural characteristics including medical conditions.

Your genes are a set of instructions for the growth and development of every cell in your body. For example, they determine characteristics such as your blood group and the colour of your eyes and hair.

However, many characteristics aren't due to genes alone environment also plays an important role. For example, children may inherit 'tall genes' from their parents, but if their diet doesn't provide them with the necessary nutrients, they may not grow very tall.

Genes are packaged in bundles called chromosomes. In humans, each cell in the body contains 23 pairs of chromosomes 46 in total.

You inherit one of each pair of chromosomes from your mother and one from your father. This means there are two copies of every gene in each cell, with the exception of the sex chromosomes, X and Y.

The X and Y chromosomes determine the biological sex of a baby. Babies with a Y chromosome (XY) will be male, whereas those without a Y chromosome will be female (XX). This means that males only have one copy of each X chromosome gene, rather than two, and they have a few genes found only on the Y chromosome and play an important role in male development.

Occasionally, individuals inherit more than one sex chromosome. Females with three X chromosomes (XXX) and males with an extra Y (XYY) are normal, and most never know they have an extra chromosome. However, females with one X have a condition known as Turner syndrome, and males with an extra X have Klinefelter syndrome.

The whole set of genes is known as the genome. Humans have about 21,000 genes on their 23 chromosomes, so the human genome contains two copies of those 21,000 (except for those on X and Y in males).

Deoxyribonucleic acid (DNA) is the long molecule found inside chromosomes that stores genetic information. It is tightly coiled into a double helix shape, which looks like a twisted ladder.

Each 'rung' of the ladder is made up of a combination of four chemicals adenine, thymine, cytosine and guanine which are represented as the letters A, T, C and G.

These 'letters' are ordered in particular sequences within your genes and they contain the instructions to make a particular protein, in a particular cell, at a particular time. Proteins are complex chemicals that are the building blocks of the body. For example, keratin is the protein in hair and nails, while haemoglobin is the red protein in blood.

There arearound six billion letters of DNA code within each cell.

As well as determining characteristics such as eye and hair colour, your genes can also directly cause or increase your risk of a wide range of medical conditions.

Although not always the case, many of these conditions occur when a child inherits a specific altered (mutated) version of a particular gene from one or both of their parents.

Examples of conditions directly caused by genetic mutations include:

There are also many conditions that are not directly caused by genetic mutations, but can occur as the result of a combination of an inherited genetic susceptibility and environmental factors, such as a poor diet, smoking and a lack of exercise.

Read more about how genes are inherited.

Genetic testing can be used to find out whether you are carrying a particular genetic mutation that causes a medical condition.

This can be useful for a number of purposes, including diagnosing certain genetic conditions, predicting your likelihood of developing a certain condition and determining if any children you have are at risk of developing an inherited condition.

Testing usually involves taking a blood or tissue sample and analysing the DNA in your cells.

Genetic testing can also be carried to find out if a foetus is likely to be born with a certain genetic condition by extracting and testing a sample of cells from the womb.

Read more about genetic testing and counselling.

The Human Genome Project is an international scientific project that involves thousands of scientists around the world.

The initial project ran from 1990 to 2003. Its objective was to map the immense amount of genetic information found in every human cell.

As well as identifying specific human genes, the Human Genome Project has enabled scientists to gain a better understanding of how certain traits and characteristics are passed on from parents to children.

It has also led to a better understanding of the role of genetics in a number of genetic and inherited conditions.

Page last reviewed: 08/08/2014

Next review due: 08/08/2016

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Genetics - NHS Choices

Y chromosome – Genetics Home Reference

Reviewed January 2010

The Y chromosome is one of the two sex chromosomes in humans (the other is the X chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The Y chromosome spans more than 59 million building blocks of DNA (base pairs) and represents almost 2 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. The Y chromosome is present in males, who have one X and one Y chromosome, while females have two X chromosomes.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The Y chromosome likely contains 50 to 60 genes that provide instructions for making proteins. Because only males have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and development. Sex is determined by the SRY gene, which is responsible for the development of a fetus into a male. Other genes on the Y chromosome are important for male fertility.

Many genes are unique to the Y chromosome, but genes in areas known as pseudoautosomal regions are present on both sex chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal regions are essential for normal development.

Genes on the Y chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.

Many genetic conditions are related to changes in particular genes on the Y chromosome. This list of disorders associated with genes on the Y chromosome provides links to additional information.

Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in the Y chromosome.

In most individuals with 46,XX testicular disorder of sex development, the condition results from an abnormal exchange of genetic material between chromosomes (translocation). This exchange occurs as a random event during the formation of sperm cells in the affected person's father. The translocation affects the gene responsible for development of a fetus into a male (the SRY gene). The SRY gene, which is normally found on the Y chromosome, is misplaced in this disorder, almost always onto an X chromosome. A fetus with an X chromosome that carries the SRY gene will develop as a male despite not having a Y chromosome.

Males with 47,XYY syndrome have one X chromosome and two Y chromosomes in each cell, for a total of 47 chromosomes. It is unclear why an extra copy of the Y chromosome is associated with tall stature, learning problems, and other features in some boys and men.

Some males with 47,XYY syndrome have an extra Y chromosome in only some of their cells. This phenomenon is called 46,XY/47,XYY mosaicism.

48,XXYY syndrome is caused by the presence of an extra X chromosome and an extra Y chromosome in a male's cells. Extra genetic material from the X chromosome interferes with male sexual development, preventing the testes from functioning normally and reducing the levels of testosterone (a hormone that directs male sexual development) in adolescent and adult males. Extra copies of genes from the pseudoautosomal region of the extra X and Y chromosome contribute to the signs and symptoms of 48,XXYY syndrome; however, the specific genes have not been identified.

Y chromosome infertility is usually caused by deletions of genetic material in regions of the Y chromosome called azoospermia factor (AZF) A, B, or C. Genes in these regions are believed to provide instructions for making proteins involved in sperm cell development, although the specific functions of these proteins are unknown.

Deletions in the AZF regions may affect several genes. The missing genetic material likely prevents production of a number of proteins needed for normal sperm cell development, resulting in an inability to father children.

Chromosomal conditions involving the sex chromosomes often affect sex determination (whether a person has the sexual characteristics of a male or a female), sexual development, and the ability to have children (fertility). The signs and symptoms of these conditions vary widely and range from mild to severe. They can be caused by missing or extra copies of the sex chromosomes or by structural changes in these chromosomes.

Rarely, males may have more than one extra copy of the Y chromosome in every cell (polysomy Y). For example, the presence of two extra Y chromosomes is written as 48,XYYY. The extra genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development, but the features of these conditions are variable.

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

You may find the following resources about the Y chromosome helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

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Y chromosome - Genetics Home Reference

Proband – Wikipedia, the free encyclopedia

Proband, proposito (male proband), or proposita (female proband)[1] is a term used most often in medical genetics and other medical fields to denote a particular subject (person or animal) being studied or reported on.[2] On pedigrees, the proband is noted with a square (male) or circle (female) shaded accordingly. It is important to denote the proband, so that the relationship to other individuals can be seen and patterns established.

In most cases, the proband is the first affected family member who seeks medical attention for a genetic disorder.[2] Among the ancestors of the proband, there may be other subjects with the manifest disease, but the proband typically refers to the member seeking medical attention or being studied, even if affected ancestors are known. Often affected ancestors are unknown due to the lack of information regarding those individuals or about the disease at the time they lived. Other ancestors might be undiagnosed due to the incomplete penetrance or variable expressivity.

The diagnosis of a proband raises the index of suspicion for the proband's relatives and some of them may be diagnosed with the same disease. Conventionally, when drawing a pedigree chart, instead of the first diagnosed person, the proband may be chosen from among the affected ancestors (parents, grandparents) from the first generation where the disease is found.

The term proband is also used in genealogy, where it denotes the root node of an ahnentafel, also referred to as the progenitor.

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Proband - Wikipedia, the free encyclopedia

Workable male sterility systems for hybrid rice: Genetics …


The exploitation of male sterility systems has enabled the commercialization of heterosis in rice, with greatly increased yield and total production of this major staple food crop. Hybrid rice, which was adopted in the 1970s, now covers nearly 13.6 million hectares each year in China alone. Various types of cytoplasmic male sterility (CMS) and environment-conditioned genic male sterility (EGMS) systems have been applied in hybrid rice production. In this paper, recent advances in genetics, biochemistry, and molecular biology are reviewed with an emphasis on major male sterility systems in rice: five CMS systems, i.e., BT-, HL-, WA-, LD- and CW- CMS, and two EGMS systems, i.e., photoperiod- and temperature-sensitive genic male sterility (P/TGMS). The interaction of chimeric mitochondrial genes with nuclear genes causes CMS, which may be restored by restorer of fertility (Rf) genes. The PGMS, on the other hand, is conditioned by a non-coding RNA gene. A survey of the various CMS and EGMS lines used in hybrid rice production over the past three decades shows that the two-line system utilizing EGMS lines is playing a steadily larger role and TGMS lines predominate the current two-line system for hybrid rice production. The findings and experience gained during development and application of, and research on male sterility in rice not only advanced our understanding but also shed light on applications to other crops.

Male reproductive development in plants involves several major developmental stages in series and along several cell lineage pathways, which include specification of stamen primordia, production of sporogenous cells, development of tapetum and microspore mother cells (MMCs), meiosis, formation of free haploid microspores, degeneration of tapetum and release of mature pollen grains (Goldberg et al. [1993]). Arrest of any of these steps can result in male sterility (MS), the failure to produce or release functional pollen grains. The phenotypic manifestations of MS may range from the complete absence of male organs, abnormal sporogenous tissues, to the inability of anther to dehisce or of pollen to germinate on compatible stigma (Chase et al. [2010]).

Evolutionarily, MS has been a subtle means by which plants prevent self-pollination and increase genetic diversity (Hanson [1991]). Over the past century, MS has facilitated the use of heterosis (or hybrid vigor) in crop production. Utilization of heterosis, the superior performance that the first generation (F1) hybrid demonstrates over its two parental lines, depends on the cost-effective production of hybrid seeds. Rice is a staple food crop for more than half of the worlds population; the use of heterosis in rice is second only to that in corn, among crop plants, and has played a significant role in further increasing rice yield after the first Green Revolution (Li et al. [2007]).

The success of hybrid rice has greatly promoted the search for and study of MS in rice. Several articles have recently reviewed the key genes and networks that determine male reproductive development, including the differentiation of sporophytic cells (Xing et al. [2011]; Feng et al. [2013]), specification of tapetum and microsporocyte cells (Zhang and Yang [2014]), and biosynthesis and regulation of sporopollenin and pollen exine development (Ariizumi and Toriyama [2011]; Liu and Fan [2013]). Mutations in such genes often result in MS in different forms, e.g. knockout mutation of CAP1, which encodes L-arabinokinase, resulted in collapsed abnormal pollens (Ueda et al. [2013]), and microsporeless anthers resulted from null mutations of MSCA1 in corn (Chaubal et al. [2003]) and MIL1 in rice (Hong et al. [2012]). As reviewed recently by Guo and Liu ([2012]) and Wang et al. ([2013b]), more than 40 MS genes have been cloned in rice. Shortly after the publication of these two reviews, several more rice fertility/sterility-related genes were reported, including genes underpinning tapetum function and hence pollen development (Liu and Fan [2013]; Ji et al. [2013]), genes required for the development of the anther and pollen (Moon et al. [2013]; Niu et al. [2013a], [b]), and genes for pollen germination and pollen tube growth (Huang et al. [2013b]). Clearly, the list is expected to grow in the near future. Although identifying genes and pathways is necessary in order to understand the underlying mechanisms in the development of the male reproductive system, not all MS mutations have practical use in hybrid crop production. This paper aims to analyze different MS systems that have been explored in hybrid rice production and summarize the latest understanding of their genetics, biochemistry, and biology. We also describe the dynamics of different MS systems in hybrid rice production in China over the past 30years.

Commercialization of any hybrid crop can only be achieved if reasonably priced technical solutions to hybrid seed production are available. In rice, hybrid seed production was first attempted using chemical hybridizing agent in the 1970s, but this approach was no longer used after MS systems became available. In order for an MS system to be workable for hybrid seed production, it must meet the following prerequisites: (1) complete and stable MS during hybrid seed production; (2) no substantial negative effect on MS and hybrid plants; (3) ability to multiply MS seeds through an intermediate genetic line (maintainer) or under particular environmental conditions; (4) ability to fully achieve fertility in hybrids. Therefore, although a number of MS systems have been generated during the past 40years, only those that met these requirements were adopted in hybrid production. So far, two distinct systems have been utilized in hybrid rice production: cytoplasmic male sterility (CMS) and environment-conditioned genic male sterility (EGMS).

Numerous CMS systems with different cytoplasm/nucleus combinations have been generated through backcross breeding. The cytoplasm and nucleus of CMS lines may originate from two different species, two different subspecies (indicajaponica), or two cultivars (indicaindica) (Virmani [1994]; Cheng et al. [2007]; Fujii et al. [2010]; Huang et al. [2013a],[b]). According to the China Rice Data Center ( webcite), a total of 13 types of CMS lines have been used in developing hybrid cultivars, constituting an annual growing area of more than ~6800ha in at least 1year from 1983 to 2012 (data before 1983 are unavailable). The cytoplasm and nucleus sources of these 13 different CMS types are summarized in Table1, with BT-CMS and Dian1-CMS used in japonica and other systems used in indica hybrid rice production.

Table 1. Major male sterility systems utilized in hybrid rice production in China1

Both BT-CMS and Dian1-CMS contain indica cytoplasm and a japonica nucleus, whereas indica hybrid rice cultivars contain cytoplasm of diverse origins, including O. rufipogon (e.g., WA-CMS), various indica cultivars (e.g., GA-CMS, ID-CMS), and one japonica genotype (i.e., K-CMS) (Table1). It is not difficult to develop japonica CMS lines using cytoplasm from O. rufipogon or other indica lines, but such CMS has no practical use because no restorer lines have been identified in japonica rice.

WA-CMS lines are the most widely deployed lines in hybrid rice production (see below). Pollen abortion in WA-CMS occurs relatively early during microspore development, mainly at the uninucleate stage (Luo et al. [2013]), resulting in amorphous aborted pollen grains (Figure1). The pollen abortion is determined by the genotype of sporophytic tissues, not by the genotype of the pollen itself. That is, aborted pollens are only produced in plants with homozygous rf (restorer of fertility) gene (s) and CMS factor (s), but not in plants that are heterozygous at the Rf locus (Figure1, pollen fertility of F1 plants). All other CMS types of indica rice, except for HL-CMS, are similar to WA-CMS and are classified as WA-CMS-like types (Table1).

Figure 1. A schematic presentation of the five well-studied rice CMS types. Abbreviations for cytoplasm sources are RWA for wild-abortive Oryza rufipogon, RRA for red-awned O. rufipogon, and RW1 for Chinese wild rice (O. rufipogon) accession W1; IBT and ILD for indica Boro-II type and Lead rice, respectively. Nucleus sources are either indica (I) or japonica (J).

Pollen development in HL-CMS lines is arrested at the binucleate stage while that of BT-CMS arrested at the trinucleate stage. In contrast to the irregular morphology in WA-CMS, the pollen grains in both HL- and BT-CMS are spherical, and are unstainable or stainable, respectively, in I2-KI solution (Li et al. [2007]). Due to their deficiency in starch accumulation, pollen grains of BT-CMS is stained lighter than normal pollen grains (Figure1; Wang et al. [2006]); the intensity of staining, however, can be rather dark in some BT-CMS lines, almost indiscriminate from that of fertile pollen grains (Li et al. [2007]). Furthermore, unlike in WA-CMS, the MS of the BT- and HL-CMS lines is genetically controlled by gametophytic tissue (i.e., the haploid microspores; hence, only half of the pollen grains in F1 plants are viable) (Figure1). Dian1-CMS lines are very similar to BT-CMS in terms of pollen abortion and fertility restoration; they are classified as BT-like CMS (Table1).

The other MS system that is widely used in hybrid rice breeding is the EGMS system, which includes the photoperiod-sensitive genic male sterility (PGMS) and temperature-sensitive genic male sterility (TGMS) lines. PGMS lines are male-sterile under natural long day conditions and male fertile under natural short day conditions (Ding et al. [2012a]), whereas TGMS lines are sterile at high temperatures and fertile at lower temperatures (Xu et al. [2011]). Some lines, such as Peiai 64S, are male sterile under both long day and high temperature conditions and are referred to as P/TGMS lines (Zhou et al. [2012]).

The majority (>95%) of the EGMS lines utilized in hybrid rice production in China were derived from three independent progenitor lines, i.e., PGMS line Nongken 58S (NK58S) and TGMS lines Annong S-1 and Zhu 1S (Si et al. [2012]; Table1). Many lines derived from NK58S were P/TGMS or even TGMS (e.g., Guangzhan 63S), but the underlying mechanism leading to such dramatic changes has yet to be revealed (Lu [2003]).

Two other CMS types have the potential to be utilized in hybrid rice production. LD-CMS was obtained by Watanabe et al. ([1968]) by performing a backcross of the japonica variety Fujisaka 5 to the Burmese rice cultivar Lead Rice, giving it indica cytoplasm and a japonica nucleus (Figure1). The pollen grains of LD-CMS can be slightly stained with I2-KI, but they cannot germinate on stigmas (Figure1). The other CMS type is CW-CMS, which has the cytoplasm of O. rufipogon and a japonica nucleus. It produces morphologically normal pollen grains that can be stained darkly with I2-KI but lacks the ability to germinate (Figure1; Fujii and Toriyama [2005]). Both LD-CMS and CW-CMS are gametophytically controlled and hence half of the pollen grains of F1 plants are viable (Figure1).

A novel type of EGMS rice, known as rPGMS (reverse PGMS), may also be useful in hybrid rice system. This rice shows normal male fertility under long day conditions (>13.5h) but is male sterile under short day conditions (<12.5h). It can be used in a two-line hybrid system by producing hybrid seeds in the tropics and subtropics (e.g., Sanya, Hainan) and multiplying seeds of rPGMS lines under long day conditions (e.g., summer season in Shanghai) (Zhang et al. [2013]).

The CMS is controlled by the interaction of cytoplasmic factors (now widely identified as mitochondrial genetic factors) and nuclear genes (Chen and Liu [2014]). As shown in Figure1, most CMS genes and their corresponding Rf genes have already been identified.

The genetic factors conditioning BT-, HL-, and WA-CMS are all chimeric genes, probably as a result of the rearrangement of the mitochondrial genome (Figure1). The BT-CMS gene, a mitochondrial open reading frame, orf79, was the first CMS gene identified (Akagi et al. [1994]) and subsequently cloned (Wang et al. [2006]) in rice. It is co-transcribed with a duplicated atp6 and hence is also known as B-atp6-orf79 (Figure1). Mitochondrial DNA analysis suggested that orf79 may also be responsible for Dian1-CMS (Luan et al. [2013]).

In HL-CMS lines, a chimeric ORF defined as atp6-orfH79 is the gene conditioning MS (Figure1). Although nucleotide sequences of orfH79 and orf79 share 98% identity, the intergenic regions between atp6-orfH79 and B-atp6-orf79 are significantly different, suggesting that atp6-orfH79 and B-atp6-orf79 diverged from a common ancestor (Yi et al. [2002]; Peng et al. [2010]; Hu et al. [2012]).

Two differentially expressed transcripts, one of them containing the ribosomal protein gene rpl5, were identified by examining the transcripts of the whole mitochondrial genomes of a WA-CMS line, Zhenshan 97A and of its maintainer, Zhenshan 97B (Liu et al. [2007]). The same group recently used rpl5 to probe the rearranged region in the mitochondrial genome and identified the WA-CMS gene, named WA352 (Wild Abortive 352), which is comprised of three rice mitochondrial genomic segments (orf284, orf224, and orf288) and one segment of unknown origin (Figure1), and encodes a 352-residue putative protein with three transmembrane segments (Luo et al. [2013]).

Previous work by Bentolila and Stefanov ([2012]), constituting the complete sequencing of male-fertile and male-sterile mitochondrial genomes, identified a WA-CMS-specific ORF, orf126, as a plausible candidate for the WA-CMS causative gene. This result is consistent with that of Luo et al. ([2013]) because orf126 is indeed part of WA352. Independently, Das et al. ([2010]) also identified rearrangements around the regions of atp6 and orfB. According to Luo et al. ([2013]), the atp6 locus is rearranged and directly linked to WA352, which is less than 20kb away from orfB in WA-CMS. Therefore, the results of these studies all corroborate one another.

The CMS gene that conditions LD-CMS has yet to be determined, but a B-atp6-orf79-like structure (L-atp6-orf79) was identified as the candidate (Figure1). In the mitochondrion of LD-CMS, there is only one copy of atp6 linked with orf79, which is different from BT-CMS and HL-CMS, the mitochondria of which retain a normal atp6 (N-atp6) in its origin position (Itabashi et al. [2009]).

No B-atp6-orf79-like structure was identified in the mitochondrion of CW-CMS, and the cytoplasmic factor (s) conditioning pollen sterility has yet to be determined (Fujii et al. [2010]).

It has been well documented that CMS can be restored by one or two Rf genes. A total of six Rf genes (Rf1a, Rf1b, Rf2, Rf4, Rf5 and Rf17) have been cloned (Figure1), and all except Rf17 are dominant.

Two fertility restoration genes, Rf1a and Rf1b, both encoding proteins containing pentatricopeptide repeat (PPR) motifs, were identified as being able to restore the fertility of BT-CMS (Kazama and Toriyama [2003]; Akagi et al. [2004]; Komori et al. [2004]; Wang et al. [2006]). Both Rf1a and Rf1b are located in the classical Rf1 locus. The rf1a allele differs from Rf1a due to a frameshift mutation that results in a truncated putative protein of 266 amino acids (Komori et al. [2004]; Wang et al. [2006]). A single-nucleotide polymorphism (SNP) of A1235-to-G causes the missense mutation of Rf1b to rf1b by substituting Asn412 for Ser (Wang et al. [2006]).

MS of HL-CMS can be restored by either Rf5 or Rf6, producing 50% normal pollen grains in F1 plants (Figure1). When both Rf5 and Rf6 are present, F1 plants may have 75% normal pollen grains (Huang et al. [2012]). Recently, the Rf5 gene was cloned and was identified to be the same gene as Rf1a or Rf1, which encodes the PPR protein PPR791 (Hu et al. [2012]). Sequencing of Rf5 and rf5 identified a single nucleotide T791-to-A alteration at the fourth PPR motif, which results in a nonsense mutation (TAT to TAA) in the HL-CMS line (Hu et al. [2012]).

WA-CMS can be restored by either Rf3 or Rf4, located on chromosome 1 and 10, respectively (Figure1). Numerous attempts have been made to delimit and ultimately clone the two genes without much success (Ahmadikhah and Karlov [2006]; Ngangkham et al. [2010]; Suresh et al. [2012]). The breakthrough was not made until very recently by Tang et al. ([2014]), who finally cloned the Rf4 gene, which also encodes a PPR protein.

Pollen fertility of LD-CMS can be restored by either Rf1 or Rf2; the latter has already been cloned (Figure1; Itabashi et al. [2009], [2011]). The Rf2 gene encodes a mitochondrial glycine-rich protein; replacement of isoleucine by threonine at amino acid 78 of the RF2 protein causes functional loss of the rf2 allele (Itabashi et al. [2011]). The CW-CMS is restored by a single nuclear gene, Rf17, which is a retrograde-regulated male sterility (rms) gene (Figure1; Fujii and Toriyama [2009]). Contrary to this finding, the same group suggested in earlier reports that two other genes, DCW11 and OsNek3, were related to pollen sterility in CW-CMS rice (Fujii and Toriyama [2008]; Fujii et al. [2009]). It is now evident that diversified mechanisms have been evolved for restoring fertility in CMS with multilayer interactions between the mitochondrial and nucleus genes (Chen and Liu [2014]).

In addition to the three major CMS types (i.e., WA-, BT-, and HL-CMS), several other CMS types were bred independently and have different cytoplasm and nucleus sources (Table1). Further studies revealed that both cytoplasm and nuclear genetic determinants are almost identical among some of them; hence, they may be classified into a common group.

First, the fertility restoration of Dian1-CMS is identical to that of BT-CMS, i.e., restorer lines of the latter are equally effective for the former, although Rf-D1 (t) was assigned for Dian1-CMS (Tan et al. [2004]). Subsequent cloning and characterization suggested that Rf-D1 is highly similar to Rf1a and has only one nucleotide difference (Zhu et al. [2009]).

Second, nine CMS types are classified as WA-like CMS (Table1) on the basis of the following observations: (1) WA352 is also identified in the GA-, D-, DA-, ID-, K-, and Y-CMS lines (Luo et al. [2013]); (2) Rf3 and Rf4 are effective for restoring the fertility of D-, DA-, ID-, GA-, Y-, and WA-CMS (Sattari et al. [2008]; Cai et al. [2014]); (3) these nine CMS types possess common mitotype-specific sequences that differ from fertile genotypes and from other CMS systems (e.g., BT-CMS, HL-CMS) (Xie et al. [2014]); and (4) they have identical or highly similar mitochondrial DNA (Luan et al. [2013]). However, we should not exclude the possibility that differences exist in their mitochondrial genomes. For example, Xu et al. ([2013]) recently indicated that male sterile cytoplasm has a marked effect on DNA methylation, which is enhanced to a much greater extent in WA- and ID-CMS than in G- and D-CMS.

Third, restorer lines containing Rf4 can often restore the fertility of BT-CMS and HL-CMS (but the opposite is not true). This effect might be explained by the following considerations: (1) Plants with Rf4 may also possess Rf1a and Rf1b. (2) The Rf4 allele has more functions than Rf1, and Rf4 itself has the ability to restore the fertility of both WA-CMS and BT-CMS. Notably, the recent cloning of Rf4 reveals that it also encodes a PPR protein, with high amino acid sequence identity with Rf1a of BT-CMS (Tang et al. [2014]).

Rice is a short-day plant; short day length accelerates panicle initiation and promotes flowering, but long day length delays or inhibits development. Likewise, relatively high temperatures promote rice growth and development. This reaction of plants to photoperiod and temperature is described as the first photoperiod/temperature reaction (FPTR, Yuan et al. [1993]). The P/TGMS lines described in this paper are those in which the male reproductive system responds to both day length and temperature, in the so-called second photoperiod/temperature reaction (SPTR).

Different EGMS lines may have very different fertility responses to photoperiod and temperature. Cheng et al. ([1996]) classified EGMS lines into three types: PGMS lines respond to either photoperiod or photoperiod-and-temperature, but not to temperature alone; TGMS lines respond to temperature, but not to photoperiod; P/TGMS lines are characterized by responding to photoperiod-and-temperature for their fertility transition.

During the past 20years, a number of EGMS lines have been identified that show genic MS under different conditions: long day (PGMS) or short day (reverse PGMS, rPGMS), high temperature (TGMS) or low temperature (rTGMS), and either long day or high temperature. In all these cases, the pollen fertility of EGMS systems is sporophytically controlled by nuclear gene (s), and the loci that control PGMS or TGMS, including rPGMS or rTGMS, have been mapped to different chromosomes (Si et al. [2012]; Sheng et al. [2013]; Zhang et al. [2013]). These mappings include PGMS genes: pms1, pms2, pms3; rPGMS genes: rpms1, rpms2, csa; TGMS genes: tms1, tms2, tms3, tms4, tms5, tms6, tms6(t), tms9; and P/TGMS genes: p/tms12-1, pms1(t). Some of these genes may be allelic and two of them, pms3 (p/tms12-1) (Ding et al. [2012a]; Zhou et al. [2012]) and csa (Zhang et al. [2013]), have been cloned.

NK58S, the first PGMS, was identified in 1973 from a Nongken58 population. It exhibits complete MS when growing under long days (day length more than 13h), but complete or partial fertility under short days (day length less than 13h) (Zhang and Yuan [1989]). However, Peiai 64S, developed from a cross between NK58S and Peiai 64 followed by backcrossing with Peiai 64, showed MS under both long day and high temperature conditions (Luo et al. [1992]). W6154S, also derived from NK58S, is a TGMS line. Zhang et al. ([1994]) identified two genes underlying the PGMS of NK58S. A study on the allelism of gene (s) for P/TGMS lines further showed that there were allelic male sterile genes between NK58S and its derivatives W6154S and Peiai 64S, but male sterile genes from the latter two are nonallelic, suggesting that NK58S has at least two genes underpinning its PGMS (Li et al. [2003]). Two recent independent studies identified the identical causative SNP for both the PGMS of NK58S (pms3, Ding et al. [2012a]) and the TGMS of Peiai 64S (p/tms12-1, Zhou et al. [2012]), although the identity of the locus containing the SNP was different (see below).

An rPGMS gene, carbon starved anther (csa), was recently cloned and may be potentially useful for diversification of the two-line hybrid rice system (Zhang et al. [2013]).

Several spontaneous TGMS mutants have been independently identified in breeding programs; more TGMS lines were selected in the progenies derived from NK58S (Si et al. [2012]). Genetic analyses indicated that the TGMS trait is under the control of single recessive genes. Among the fine-mapped TGMS genes, those of Annong S-1 (tms5), Guangzhan 63S (ptgms2-1), and Zhu 1S (tms9) are all located on chromosome 2. Whereas tms5 and ptgms2-1 were delimited to a partially overlapped region, tms9 was fine-mapped to a different segment near that of ptgms2-1/tms5 (Sheng et al. [2013]). Candidate genes were proposed for tms5 (OsNAC6; Yang et al. [2007]) and ptgms2-1 (a ribonuclease Z homolog, RNZ; Xu et al. [2011]), but none were suggested for tms9 (Sheng et al. [2013]). Our recent study, however, demonstrated that Annong S-1, Guangzhan 63S and Zhu 1S carry allelic TGMS genes (i.e. tms5, ptgms2-1, and tms9 are allelic), and further characterization of more than 300 non-EGMS and EGMS lines suggested that an identical nonsense mutation of the RNZ gene, i.e. RNZm.conditions the TGMS of Guangzhan 63S, Zhu 1S, Annong S-1, and a number of other TGMS lines (Zhang et al. [2014]).

Anther development in rice occurs over 14 stages (Zhang and Wilson [2009]), and the specification, development, and degradation of the anther are tightly regulated by various genes and pathways. Dysfunction of any gene may result in MS (Suzuki [2009]; Wilson and Zhang [2009]; Ariizumi and Toriyama [2011]; Feng et al. [2013]).

The development of pollen and degradation of the endothecium, middle layer, and tapetal cells are illustrated in Figure2. The tapetum is the nursing tissue inside the anther and plays a crucial role in the formation and development of pollen grains (Suzuki [2009]; Ariizumi and Toriyama [2011]). In wild-type plants, tapetum undergoes cellular degeneration by programmed cell death (PCD) and completely disappears by the time the mature pollen grains form. PCD is often observed in anther tissues by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. Slight differences have been reported regarding the commencement of tapetal PCD in rice: One group (Ji et al. [2013]; Luo et al. [2013]) detected PCD as early as stage 8a (the dyad stage), whereas others (Li et al. [2006]; Ding et al. [2012a]) observed the earliest PCD occurring at stage 8b (the tetrad stage) or noted that it peaked at stage 9 (young microspore stage). The correct timing of tapetal PCD is important, and premature or delayed PCD is often associated with MS. Unlike most other rice MS mutants, which have delayed tapetal PCD (Li et al. [2006]; Ji et al. [2013]), certain EGMS and WA-CMS rice have premature tapetal PCD (Ding et al. [2012a]; Luo et al. [2013]; Figure2).

Figure 2. A schematic presentation of anther and pollen development in wild type (WT) rice, wild-abortive CMS (WA-CMS) rice, temperature- and photoperiod -sensitive genic male sterile (TGMS and PGMS) rice. Stage demarcation and developmental features of WT rice are adopted from Zhang and Wilson ([2009]); those of WA-CMS, TGMS and PGMS are according to Luo et al. ([2013]), Ku et al. ([2003]), and Ding et al. ([2012a]), respectively. Dots represent the DNA fragmentations detected by TUNNEL assay in tapetal cells undergoing programmed cell death. AP, aborted pollen; BP, binucleate pollen; E, epidermis; En, endothecium; ML, middle layer; T, tapetum; MMC, microspore mother cell; MC, meiotic cell; DY, dyad; Td: tetrad; MP, mature pollen.

The TGMS lines of Annong S-1, Xian 1S, and Guangzhan 63S have empty anthers (Ku et al. [2003]; Peng et al. [2010]; Xu et al. [2011]). Premature tapetal PCD initiates as early as the microspore mother cell (MMC) stage (stage 6) and continues until the tapetal cells are completely degraded in Annong S-1 grown under high temperature conditions (Ku et al. [2003]). The premature tapetal PCD resulted in early degradation of the tapetum, causing a decline in the supply of nutrition and other components (e.g. sporopollenin) to microspores, which were ruptured around stage 9. Consequently, no pollen grains were seen in the pollen sac in TGMS lines (Figure2).

Analysis of the PGMS line NK58S grown under long-day conditions demonstrated that tapetal PCD was already apparent at stage 7 and became intense from stage 8a to stage 9, much earlier than in NK58 (Ding et al. [2012a]). The premature tapetal PCD in NK58S resulted not only in pollen abortion but also incomplete degradation of tapetal cells at later stages (Figure2).

The different timings of premature tapetal PCD in TGMS and PGMS lines entail distinct consequences on pollen development in these two types (i.e., no pollen is formed in the pollen sac in TGMS lines and pollen abortion occurs in PGMS lines) (Figure2). However, it remains unclear whether the premature tapetal PCD is induced under MS-inducing conditions, because neither the PGMS gene nor the TGMS gene is involved directly or indirectly in any known PCD pathway.

In WA-CMS line Zhenshan 97A, tapetal PCD was also observed as early as stage 7 (Figure2), although it was not detected until stage 8a in its maintainer line Zhenshan 97B (Luo et al. [2013]). Tapetal PCD in WA-CMS rice started at the same stage as in PGMS rice, however, TUNEL assay indicated that DNA fragmentation only persisted to stage 9 in tapetal cells. Degradation of tapetal cells started as early as stage 8b, at which stage cytological observation showed debris was leaking from tetrads or tapetal cells. Consequently, tapetal cells degraded earlier than in wild type rice, and abnormal development of microspores could already be seen at stage 9 (Luo et al. [2013]; Figure2). The molecular mechanism leading to premature tapetal PCD in WA-CMS rice is well explained (see below).

In the BT-CMS system, CMS is known to be caused by a cytotoxic peptide, ORF79, encoded by a mitochondrial dicistronic gene B-atp6-orf79. ORF79 is a transmembrane protein; it is toxic to Escherichia coli (Wang et al. [2006]) and is also toxic to plant regeneration when it targets the mitochondria (Kojima et al. [2010]). ORF79 is accumulated specifically in microspores, despite its constitutive expression (Wang et al. [2006]), which provides a tight correlation between its accumulation and the phenotype of gametophytic MS. The molecular mechanism that regulates the expression of ORF79 and the way in which it causes the arrest of microspore development at the trinucleate stage are unknown.

BT-CMS is restored by two related PPR motif genes, Rf1a and Rf1b, by blocking ORF79 production through distinct modes of mRNA silencing: endonucleolytic cleavage of the dicistronic B-atp6-orf79 mRNA by RF1A and degradation by RF1B. In the presence of these two restorers, the Rf1a gene has an epistatic effect over the Rf1b gene in mRNA processing (Wang et al. [2006]). Further studies suggested that the RF1 protein mediates cleavage of the dicistronic mRNA by binding to the intergenic region, and the processed orf79 transcripts are degraded and unable to associate with ribosome. As a result, the orf79 expression is drastically reduced due to the processing of atp6-orf79 transcripts (Kazama et al. [2008]).

The mitochondrial dicistronic gene atp6-orfH79 is responsible for HL-CMS (Peng et al. [2010]), as proposed by Wang et al. ([2002]). Transcripts of orf79 and orfH79 differ in only five nucleotides, each of which results in distinctly different codon (Peng et al. [2010]). Like orf79, orfH79 is constitutively expressed; however, accumulation of ORFH79 is not limited to microspores as it is for orf79 in BT-CMS. Rather, it is accumulated mainly in the mitochondria in both vegetative and reproductive tissues, preferentially in sporogenous cells and root tips (Peng et al. [2010]). ORFH79 impairs mitochondrial function through its interaction with P61, a subunit of electron transport chain (ETC) complex III in HL-CMS rice (Wang et al. [2013a]). The interaction of ORFH79 and P61 significantly reduces the activity of ETC III through an as-yet-unknown mechanism, impairs the electron transport efficiency, and down-regulates the production of ATP. Concomitantly, more reactive oxygen species (ROS) are produced accompanying increased electron leakage from the ETC (Wang et al. [2013a]). The observations of increased ROS and preferential accumulation of ORFH79 in sporogenous cells are in accordance with a study that detected PCD in microspores of the HL-CMS line Yuetai A (Li et al. [2004]).

Unlike the RF1A-binding to B-atp6-orfH79 transcript, RF5 (the same protein of RF1A) is unable to bind to atp6-orfH79 transcript directly, due to its divergent intergenic region. Instead, a RF5s partner protein, GRP162, can bind to the atp6-orfH79 through an RNA recognition motif. These two proteins interact physically with each other in the so-called restoration of fertility complex (RFC), which can cleave atp6-orfH79 at a site 1169 nucleotides away from the atp6 start codon (Hu et al. [2012]). Additional components are predicted to participate in the RFC, because neither RF5 nor GRP162 can cleave the mRNA; it remains to be determined which factor of the RFC possesses the capacity as an endoribonuclease to process atp6-orfH79.

Another gene, Rf6, can also restore the fertility of HL-CMS, but little is known regarding its identity or the mechanism leading to fertility restoration (Huang et al. [2012]).

MS in WA-CMS rice is caused by WA352, which interacts with a nuclear-encoded integral protein of the inner mitochondrial membrane, OsCOX11. COX11 proteins are essential for the assembly of cytochrome c oxidase; they display high levels of conservation among eukaryotes and play a role in hydrogen peroxide degradation (Banting and Glerum [2006]). A significantly increased amount of ROS was observed in the tapetum of WA-CMS line Zhenshan 97A, but not in its maintainer, at the MMC stage (Luo et al. [2013]). Hence, it is assumed that the elevation of ROS in WA-CMS line, as a result of the interaction of WA352 with OsCOX11, prevents the normal function of OsCOX11 in H2O2 degradation. The excessive amount of ROS could further affect the mitochondrial membrane permeability and promote Cyt c release into the cytosol, triggering PCD (Luo et al. [2013]).

Both OsCOX11 and WA352 are constitutively expressed; however, while OsCOX11 protein is accumulated in all tissues, WA352 protein was detected only in anthers, not in leaves. In the anthers, WA352 was observed mainly in tapetal cells at the MMC stage and diminished after the meiotic prophase I stage. The tissue specificity and accumulation duration of WA352 are in good accordance with the occurrence of tapetal PCD as detected by TUNEL assay, the earliest PCD being observed as early as stage 7 of anther development (Figure2; Luo et al. [2013]). However, it is not known why WA352 only accumulates in tapetal cells at the MMC stage. Further studies are needed to uncover the molecular mechanism and genetic factor (s) regulating time-specific protein accumulation.

WA-CMS can be restored by either Rf3 or Rf4 (Figure1). The amounts of WA352 transcripts in the Rf4-carrying lines with WA-CMS cytoplasm were decreased to ~2025% of those in the WA-CMS line without Rf4, but were not affected in the Rf3-carrying lines. WA352 was undetectable in either Rf3- or Rf4-carrying young anthers (Luo et al. [2013]). These observations suggest different mechanisms of male fertility restoration be deployed by the two Rf genes: RF4 may cleave the WA352 transcript and RF3 may suppress its translation. In this regard, RF4 may function like that of RF1B, which mediates the degradation of atp6-orf79 mRNA, whereas RF3s mode of action would be distinctly different from those of RF1A and RF1B (see above).

Fertility of the LD-CMS can be restored by either Rf1 or Rf2 (Figure2). Although LD-CMS rice also possesses a chimeric atp6-orf79 dicistronic gene, L-atp6-orf79 (Figure2), the CMS in LD-cytoplasm is not caused by the accumulation of ORF79. The induction and restoration of LD-CMS are different from those in BT-CMS (Itabashi et al. [2009]). The Rf2 gene has already been cloned and is known to encode a mitochondrial glycine-rich protein, but the mechanism of CMS restoration has yet to be determined (Itabashi et al. [2011]).

As in LD-CMS, the cytoplasmic genetic factor that causes MS in CW-CMS has not been identified. However, its restorer of fertility gene, Rf17, is known to encode a 178-aa mitochondrial protein of unknown function. Rf17 is considered to be an rms gene, because its expression is regulated by the cytoplasmic genotype. The low expression of RMS in a restorer line of CW-CMS, probably due to a SNP in its promoter region, is speculated to restore compatibility between the nucleus and mitochondria, leading to male fertility (Fujii and Toriyama [2009]).

As mentioned above, a noncoding RNA was recently identified to underpin the PGMS of NK58S (pms3) and TGMS of Peiai 64S (p/tms12-1), with a common CG SNP as the causative element of P/TGMS (Ding et al. [2012a]; Zhou et al. [2012]). However, the functional element of this locus and its role in P/TGMS development were elucidated quite differently by the two groups.

Ding et al. ([2012a]) showed that the locus encodes a long noncoding RNA (lncRNA) designated LDMAR (long day-specific male fertility associated RNA), and they argued that a sufficient amount of LDMAR is essential for male fertility under long day conditions. The low abundance of LDMAR transcripts, rather than the CG SNP, is responsible for the PGMS of NK58S, because overexpression of the LDMAR transcript of NK58S restored the fertility of NK58S under long day conditions. They indicated that the low expression of LDMAR in NK58S is due to increased methylation in the promoter region, compared with NK58 (Ding et al. [2012a]). In a later study, they identified in the promoter region of LDMAR a siRNA called Psi-LDMAR, which is more abundant in NK58S than its wild type line (Ding et al. [2012b]). They suggested that the enhanced methylation in the LDMAR promoter region induced by the greatly enriched PsiLDMAR repressed the expression of LDMAR. However, several puzzles remain: First, as the authors noted, Psi-LDMAR is produced mainly in leaves, but regulation of fertility should reside in panicles (Ding et al. [2012b]); Second, the role of the CG SNP in increasing methylation of the promoter directly, or indirectly through the generation of Psi-LDMAR, was not addressed.

After identifying the lncRNA locus, Zhou et al. ([2012]) further narrowed down its functional form to a small, 21-nt RNA, designated as osa-smR5864w and osa-smR5864m for the wild-type and mutant allele, respectively. The small RNA may be a product of a 136-nt intermediate precursor. They speculated that osa-smR5864w may be the functional form and regulate male development under sterility-inducing conditions by cross-talking between the genetic networks and environmental conditions. However, no gene known to be involved in anther and pollen development has been shown to be the target of osa-smR5864w.

In addition to offering different explanations for the functional identity of the lncRNA locus, Ding et al. ([2012a]) and Zhou et al. ([2012]) made the following different observations: (1) LDMAR is expressed in all tissues and is relatively higher in panicles, whereas osa-smR5864w is mainly expressed in panicles; (2) Expression of LDMAR in NK58 is significantly higher under long days than under short days, and is significantly higher in NK58 than in NK58S under any day length, while expression of osa-smR5864w is almost independent of growing conditions. Consequently, Ding et al. ([2012a]) argued that occurrence of PGMS under long day resulted from lower expression of LDMAR rather than from the CG SNP; Zhou et al. ([2012]) inferred that it was the function rather than the amount of osa-smR5864w that determined PGMS in NK58S and TGMS in Peiai 64S.

Further studies will verify which hypothesis is correct, but the authors of this review are inclined to agree with Zhou et al. ([2012]) for the following reasons. (1) The functional importance of the CG SNP is explained in osa-smR5864w and osa-smR5864m, but it is very speculative in LDMAR. (2) The spatial expression of osa-smR5864w is more relevant to its function than is the spatial expression of LDMAR. (3) The possibility that LDMAR is a precursor of small RNA was not excluded. Indeed, Ding et al. ([2012a]) predicted and verified by RT-PCR that three small RNAs could be processed from a stem-loop structure involving 145 bases of LDMAR, and the smRNA-1 with the CG SNP is exactly the same as osa-smR5864.

The RNase Z enzyme is a highly conserved single-chain endoribonuclease that is expressed in all living cells. There are two classes of RNase Z proteins, long RNase ZL and short RNase ZS (Vogel et al. [2005]). RNase Z catalyzes the hydrolysis of a phosphodiester bond, producing 3-hydroxy and 5-phospho termini as it participates in tRNA maturation by cleaving off a 3 trailer sequence (Mayer et al. [2000]). The first RNase Z gene was cloned from Arabidopsis (Schiffer et al. [2002]); studies of homologous genes in various species have revealed that RNase Z could cleave a broader spectrum of substrates, including coding and noncoding RNAs (Xie et al. [2013]).

In plants, RNase Z is described using a prefix for the species, followed by TRZ (e.g., AthTRZ and OsaTRZ are the RNase Z genes in Arabidopsis and rice, respectively) (Fan et al. [2011]). The rice genome has three RNase Z genes: OsaTRZ1 (LOC_Os02g12290) and OsaTRZ2 (LOC_Os09g30466) encoding RNase ZS, and OsaTRZ3 (LOC_Os01g13150) encoding RNase ZL (Fan et al. [2011]). OsaTRZ2 contributes to chloroplast biogenenesis and homozygous OsaTRZ2 mutants are albino with deficient chlorophyll content due to the arrest of chloroplast development at an early stage (Long et al. [2013]). As indicated above, a nonsense mutation of OsaTRZ1 (RNZm) could be responsible for the TGMS traits in rice (Zhang et al. [2014]). Although it is unclear how this mutation leads to TGMS, the following observations in other species suggest a logical pathway by which the RNZm mutation could result in TGMS. First, the Arabidopsis genome has four RNase Z genesAthTRZ1 and AthTRZ2 for RNase ZS, and AthTRZ3 and AthTRZ4 for RNase ZLbut only the chloroplast-localized AthTRZ2 is essential. Deletions of the other three are not lethal (Canino et al. [2009]), suggesting that the null mutation of OsaTRZ1 will also not be lethal for rice development, a phenomenon that fits RNZm mutants. Second, it has been proven that conditional knockout at gametogenesis of Drosophila RNZ leads to thinner testes and lack of post-meiotic germ cells (Xie et al. [2013]), a phenomenon similar to that observed in TGMS rice: premature degeneration of tapetal cells and lack of pollen in the pollen sac (Figure2).

Because the function of TRZ genes has been assigned recently, very limited references are available for a thorough judgment of the possible functions of OsaTRZ1 and its involvement in male gametophyte formation. Further studies are needed to unveil the molecular mechanism of TGMS and to elucidate the functions and working mechanisms of TRZ1 genes in plants in general and in rice in particular.

Epigenetic regulation has recently been identified to play an important role in gene expression. DNA methylation is known to play a role in fertility transformation of rice P/TGMS (Ding et al. [2012b]). In addition, Chen et al. ([2014]) further observed that the DNA methylation level of P/TGMS line Peiai 64S was lower under low temperatures and short-day conditions (associated with fertility) than under high temperatures and long-day conditions (associated with sterility), suggesting that DNA methylation may be involved in the sterilityfertility transition of Peiai 64S in two different environmental profiles. Similarly, Xu et al. ([2013]) detected DNA methylation sites that were specific to CMS lines or maintainer lines (B lines), implying a specific relationship between DNA methylation at these sites and male-sterile cytoplasm, as well as a relationship with MS. Furthermore, Xu et al. ([2013]) demonstrated that DNA methylation was markedly affected by male-sterile cytoplasms (i.e., WA- and ID-type cytoplasms affected methylation to a much greater degree than did G- and D-type cytoplasms, although there were few differences at the DNA level). Therefore, studies on epigenetic regulation may increase our understanding of the mechanisms regulating MS and restoration.

Since the first WA-CMS-based hybrid rice was commercialized in the 1970s in China, several hundred CMS and EGMS lines have been developed, and some of them are currently or were once used in rice production. Although it is known that WA-CMS is the most widely used CMS in China (Cheng et al. [2007]) and in India (Khera et al. [2012]), so far no report has documented the dynamic changes of different MS systems in rice production. The China Rice Data Center ( webcite) has kept records of the annual planting area of rice cultivars grown in areas of at least ~6800ha from 1983 to the present day. Therefore, we are able to analyze the growing areas under hybrid rice cultivation over the past 20years (19832012). The following is the information extracted from the original data.

Two-line system hybrid rice was not commercialized until 1993; however, it has since played a steadily larger role in hybrid rice production (Figure3a). In 2012, two-line system hybrid rice already covered a total growing area of ~3.3 million ha, about one-third of the total hybrid rice growing area (~10 million ha) (Figure3a) (Note: only the hybrids that had been grown in areas more than 50,000ha were included in Figure3).

Figure 3. Planting areas covered by different types of hybrid rice in China (19832012).a, Hybrids based on BT-, HL-, and WA-CMS lines as well as EGMS (environment-conditioned genic male sterility). b, Hybrids based on different CMS types with similar features to WA-CMS. For definition of different CMS types see Table1. Note the data were composed of hybrid rice cultivars that had grown in more than 50,000ha (1983 to 2012) in this figure, cultivars with less growing area were not included.

In order to avoid the genetic vulnerability such as the crop failure of hybrid corn based on T-CMS in the 1970s, Chinese rice breeders from the very beginning have been trying to develop new types of CMS lines and to diversify the cytoplasm sources of these lines. Hence, ~15 new CMS sources other than WA-CMS have been developed and deployed in hybrid rice production. These sources may be classified into three primary groups: BT- and BT-like CMS, HL-CMS, and WA- and WA-like CMS (Table1).

BT-CMS-based japonica hybrid rice was successfully developed in the 1970s, only a few years after WA-CMS-based indica hybrids. However, the planting area was very limited compared with the latter (Figure3a). Within the BT- and BT-like category, Dian1-CMS hybrids are steadily replacing BT-CMS hybrids; the former now comprise ~90% of cultivation (data not shown).

Within the WA-CMS and the WA-CMS-like categories, there are more than a dozen subtypes of CMS lines. Although WA-CMS still dominates among the subtypes, its absolute dominance has been diminishing since the mid-1990s, and now it represent less than 55% of the total CMS-based hybrid rice (Figure3b). Indeed, this category represents almost the same proportion of all CMS rice because BT- and HL-CMS have a very low percentage of the total CMS (Figure3a).

CMS was used initially in the development of hybrid rice in the so-called three-line hybrid system, but EGMS is becoming more popular in hybrid rice production since the two-line hybrid system, in which the EGMS lines are used, has advantages of a wider range of restoring lines, more freely combinations and simple breeding program. CMS is conditioned by chimeric recombinant mitochondrial genes; the fertility of CMS lines may be restored by Rf genes. EGMS is underpinned by genes for non-coding RNA, transcriptional factors and RNA-processing enzymes. Different MS systems for rice have undergone dynamic changes in practical application in China.

B line: Maintainer line

CMS: Cytoplasmic male sterility

csa: Carbon starved anther

EGMS: Environment-conditioned genic male sterility

ETC: Electron transport chain

F1: First generation

FPTR: First photoperiod/temperature reaction

LDMAR: Long day specific male fertility associated RNA

lncRNA: Long non-coding RNA

lncRm: lncR with C-to-G SNP that underpins the PGMS phenotype

MMCs: Microspore mother cells

MS: Male sterility

NK58: Nongken58

P/TGMS: Photoperiod-and temperature-sensitive genic male sterility

PCD: Programmed cell death

PGMS: Photoperiod-sensitive genic male sterility

PPR: Pentatricopeptide repeat

Rf: Restorer of fertility gene

RFC: Restoration of fertility complex

RMS: Retrograde-regulated male steriity

RNZ: Ribonuclease Z homolog

RNZm: OsaTRZ1 carrying a null mutation that underpins the TGMS phenotype

ROS: Reactive oxygen species

rPGMS: Reverse PGMS

rTGMS: Reverse TGMS

SNP: Single-nucleotide polymorphism

SPTR: Second photoperiod/temperature reaction

TGMS: Temperature-sensitive genic male sterility

TUNEL: Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling

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Workable male sterility systems for hybrid rice: Genetics ...

Sensorineural deafness and male infertility – Genetics …

Reviewed April 2010

Sensorineural deafness and male infertility is a condition characterized by hearing loss and an inability to father children. Affected individuals have moderate to severe sensorineural hearing loss, which is caused by abnormalities in the inner ear. The hearing loss is typically diagnosed in early childhood and does not worsen over time. Males with this condition produce sperm that have decreased movement (motility), causing affected males to be infertile.

The prevalence of sensorineural deafness and male infertility is unknown.

Sensorineural deafness and male infertility is caused by a deletion of genetic material on the long (q) arm of chromosome 15. The signs and symptoms of sensorineural deafness and male infertility are related to the loss of multiple genes in this region. The size of the deletion varies among affected individuals. Researchers have determined that the loss of a particular gene on chromosome 15, the STRC gene, is responsible for hearing loss in affected individuals. The loss of another gene, CATSPER2, in the same region of chromosome 15 is responsible for the sperm abnormalities and infertility in affected males. Researchers are working to determine how the loss of additional genes in the deleted region affects people with sensorineural deafness and male infertility.

Read more about the CATSPER2 and STRC genes and chromosome 15.

Sensorineural deafness and male infertility is inherited in an autosomal recessive pattern, which means both copies of chromosome 15 in each cell have a deletion. The parents of an individual with sensorineural deafness and male infertility each carry one copy of the chromosome 15 deletion, but they do not show symptoms of the condition.

Males with two chromosome 15 deletions in each cell have sensorineural deafness and infertility. Females with two chromosome 15 deletions in each cell have sensorineural deafness as their only symptom because the CATSPER2 gene deletions affect sperm function, and women do not produce sperm.

These resources address the diagnosis or management of sensorineural deafness and male infertility and may include treatment providers.

You might also find information on the diagnosis or management of sensorineural deafness and male infertility in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

You may find the following resources about sensorineural deafness and male infertility helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

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Cloning Myths – Learn Genetics

In What is cloning? we learned what it means to clone an individual organism. Given its high profile in the popular media, the topic of cloning brings up some common, and often confusing, misconceptions.

Let's say you wanted a clone to do your homework. After reviewing What is Cloning? and Click and Clone, you've figured out, generally, how to make a clone. Knowing what you know, do you think this approach would really help you finish your homework...this decade?

A common belief is that a clone, if created, would magically appear at the same age as the original. This simply isn't true. You remember that cloning is a way to create an embryo, not a full-grown individual. The embryo, once created, must develop exactly the same way as a regular embryo made by joining egg and sperm. Your clone would need a surrogate mother and ample time to grow and fully develop into an individual.

Your beloved cat Frankie has been a loyal companion for years. Recently, though, Frankie has been showing signs of old age, and you realize that your friend's days are numbered. You can't bear the thought of living without her, so you contact a biotechnology company that advertises pet cloning services. For a fee, this company will clone Frankie using DNA from a sample of her somatic cells. You're thrilled: you'll soon have a carbon copy of Frankiewe'll call her Frankie #2and you'll never have to live without your pal! Right?

Not exactly. Are you familiar with the phrase "nature versus nurture?" Basically, this means that while genes help determine traits, environmental influences have a considerable impact on shaping an individual's physical appearance and personality. For example, do you know any identical twins? They are genetically the same, but do they really look and act exactly alike?

So, even though Frankie #2 is genetically identical to the original Frankie, she will grow and develop in a completely different environment than the original Frankie, she will have a different mother, and she will be exposed to different experiences throughout her development and life. Therefore, there is only a slim chance that Frankie #2 will closely resemble the Frankie you know and love.

Another difference between a clone and the original is the mitochondria. Mitochondria are organelles that sit inside nearly every cell. Their job is to burn fuel (from the food we eat) to make energy. Mitochondria have their own chromosome, made of DNA and divided into genes, and they divide as our cells divide.

We get our mitochondria from our mothers. Egg cells are packed with mitochondria, which are copied and distributed to new cells as they form. When a clone is made using nuclear transfer, the egg cell that's used to receive the donor nucleus is already filled with mitochondria contributed by the egg donor. As the clone develops, its cells will be filled with these mitochondriaand their genesrather than the mitochondria from the DNA donor.

Nature vs. Nurture. Find out why twins become increasingly different as they age in Epigenetics.

Clones can be made in the lab through artificial embryo twinning or nuclear transfer. But these aren't the only ways to make a clone.

Clones are simply identical genetic copies. Many organisms reproduce through cloning as a matter of course, through a process called asexual reproduction. Bacteria, yeast, and single-celled protozoa multiply by making copies of their DNA and dividing in two. Redwood and aspen trees send up shoots from their roots, which grow into trees that are genetically identical to the parent.

In the animal world, the eggs of female aphids grow into identical genetic copies of their motherwithout being fertilized by a male. If a starfish is chopped in half, both pieces can regenerate, forming two complete, genetically identical individuals. Even mammals form natural clones: identical twins are a common example in many species.

Learn more about Sexual and Asexual Reproduction.

Humans have been cloning plants for at least a couple thousand years. Many of the fruits we eatincluding bananas, grapes, and applescome from artificially created clones. Unlike the complex process of cloning a mammal, cloning a plant can be as simple as cutting a branch from one tree and grafting it onto another.

Animal cloning also has a long history. Artificial embryo twinning, which involves dividing an early embryo to form separate, genetically identical organisms, was first done in a vertebrate over 100 years ago. And the first successful nuclear transfer was done in a frog in the 1970s.

Learn more about The History of Cloning.

While animal cloning still has a high failure rate, and some well-known clones (including Dolly the sheep) have had health problems, clones are not necessarily "damaged." Many live long, healthy lives. One racing mule clone was at one time ranked third in the world. And a barrel-racing horse clone was not only born healthy, but at two years old he was also collecting a stud fee of $4,000 for his owners.

One reason for cloning's high failure rate seems to be incomplete resetting of the somatic cell's DNA. During egg and sperm formation, DNA is "reset" to a baseline or embryonic state. As the embryo develops, cells begin to differentiate into muscle, nerve, liver, and other types. Part of the differentiation process involves adding and removing chemical tags on the DNA, which keeps genes turned "on" that are necessary for the function of that cell type and keeps others turned "off."

Learn more about this process in Epigenetics.

APA format: Genetic Science Learning Center (2014, June 22) Cloning Myths. Learn.Genetics. Retrieved September 25, 2015, from MLA format: Genetic Science Learning Center. "Cloning Myths." Learn.Genetics 25 September 2015 <> Chicago format: Genetic Science Learning Center, "Cloning Myths," Learn.Genetics, 22 June 2014, <> (25 September 2015)

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Hormone and genetic study in male to female transsexual …


Data of the literature demonstrated controversial results of a correlation between transsexualism and genetic mutations.

To evaluate the hormone and gene profile of male-female (M-F) transsexual.

Thirty M-F transsexuals aged 24-39. Seventeen had already undergone sex reassignment surgery, 13 were awaiting. All subjects had been undergoing estrogen and antiandrogen therapy. We studied hormones of the hypothalamus- pituitary-testicular axis, thyroid and adrenal profile, GH basal and after GHRH stimulation, IGF-I. The gene study analyzed SRY, AR, DAX1, SOX9, AZF region of the Y chromosome.

Pre-surgery subjects had elevated PRL, reduced testosterone and gonadotropins. Post-surgery subjects showed reduced androgens, a marked increase in LH and FSH and normal PRL. Cortisol and ACTH were similar to reference values in pre- and post-surgery patients. There was a marked increase in the baseline and post-stimulation GH values in 6 of the 13 pre-surgery patients, peaking at T15. IGF-I was similar to reference values in both groups except for one post-surgery patient, whose level was below the normal range. There were no polymorphisms in the amplified gene region for SOX9, and a single nucleotide synonimous polymorphism for DAX1. No statistically significant differences were seen in the mean of CAG repeats between controls and transsexual subjects. SRY gene was present in all subjects. Qualitative analysis of the AZFa, AZFb, and AZFc regions did not reveal any microdeletions in any subject.

This gender disorder does not seem to be associated with any molecular mutations of some of the main genes involved in sexual differentiation.

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Hormone and genetic study in male to female transsexual ...

Are People Born Gay? Genetics and Homosexuality


There is a common belief among liberals that people are born either gay or straight. Conservatives tend to believe that sexual orientation is actually sexual preference, which is chosen by the individual. This page represents a review of the scientific literature on the basis for homosexual orientation.

Are people born gay or straight? Much of the current media sources assume the question is a solved scientific problem with all the evidence pointing toward a biological (probably genetic) basis for a homosexual orientation. Contrary to this perception, the question has been poorly studied (or studied poorly), although there is some evidence on both sides of question. In addition, many of the initial studies, which were highly touted by the media as "proof" for a biological basis for homosexuality, have been contradicted by later, more thorough studies. This evidence falls into four basic categories:

Until a few years ago, sexual orientation used to be called sexual preference. Obviously, the two terms denote significant differences in the the manner by which sexuality develops. A preference is something that is chosen, whereas orientation is merely something that defines us. The differences are potentially important regarding how the law applies to those who are gay. If homosexuality is not chosen, but actually is a biologically-determined characteristic over which we have no choice, then laws should not treat gays and straights differently, since homosexuality would be equivalent to one's race, over which we have no control.

Since sexual attraction begins in the brain, researchers first examined the question of sexual orientation by comparing the anatomy of brains from males and females. These studies showed that male and female brains showed sexual dimorphism in the pre-optic area of the hypothalamus, where males demonstrated a greater than two-fold difference in cell number and size compared to females.1 A second study found that two of four Interstitial Nuclei of the Anterior Hypothalamus (INAH) were at least twice as large in males as females.2 Since the INAH was involved in sexual dimorphism, it was hypothesized by Simon LeVay that there might be differences in this region in heterosexual vs. homosexual men. Postmortem examination of the brains of AIDS patients vs. control male subjects (presumed to be heterosexual) showed that the presumably heterosexual men exhibited INAH3 that were twice the size of both females and presumably homosexual men who had died of AIDS.3 The study has been criticized for its uncertainty of sexual orientation of the subjects, and potential complications caused by the AIDS virus (which does infect the human brain), and also by lowered testosterone levels found in AIDS patients. A popularized Newsweek cover story, "Is This Child Gay?"4 characterized LeVay as a "champion for the genetic side," even though the study involved no genetic data at all.

A subsequent study by Byne, et al. examined the question of INAH3 size on the basis of sex, sexual orientation, and HIV status.5 The study found large differences in INAH3 volume on the basis of sex (with the male INAH3 being larger than the female INAH3). However, the volume of IHAH3 was decreased in male heterosexual men who had contracted AIDS (0.108 mm3 compared with 0.123 mm3 in male controls). There was no statistically significant difference between IHAH3 sizes of male heterosexuals vs. male homosexuals who had contracted AIDS (0.108 mm3 and 0.096 mm3, respectively). The study also found that there were no differences in the number of neurons in the INAH3 based upon sexual orientation, although researchers found significant differences between males and females, as in other studies.5 It was obvious from this study that LeVay's study was fatally flawed due to the AIDS complication, and that there were no differences in the INAH3 based upon sexual orientation.

The role of the hypothalamus in sexual orientation was further studied by Swaab, et al. Other researchers had hypothesized that differentiation of the hypothalamus occurred before birth. However, Swaab's study showed that the sexually dimorphic nucleus (SDN) of more than 100 subjects decreased in volume and cell number in the females only 2-4 years postnatal. This finding complicated the findings of the brain studies, since not only chemical and hormonal factors, but also social factors, might have influenced this process.6

A study by Allen and Gorski examined the anterior commissure of the brain, finding that females and homosexual males exhibited a larger size than heterosexual males.7 However, later studies using larger sample sizes found no such differences.8

Complicating the issue of brain differences between homosexuals and heterosexuals is the problem that sexual experiences themselves can affect brain structure.9 So, the question will always be whether homosexual practice changes the brain or whether the brain results in homosexual practice.

Since sexual differentiation occurs within the womb, as a result of hormonal influences, it has been hypothesized that homosexuality may result from a differential hormone balance in the wombs of those who eventually exhibit a homosexual orientation. Since hormonal levels within the womb are not available, proxies for hormonal influences have been used to examine the question of how hormonal influences might impact sexual orientation. These proxies include differences in skeletal size and shape, including the ratio of the long bones of the arms and legs relative to arm span or stature and the hand bones of adults (the ratio of the length of the various phalanges).

Studies have shown that ratios of digit length are predictors of several hormones, including testosterone, luteinizing hormone and estrogen.10 In women, the index finger (2D, second digit) is almost the same length as the fourth digit (4D). However, in men, the index finger is usually shorter than the fourth. It has been shown that this greater 2D:4D ratio in females is established in two-year-olds. It has been hypothesized that the sex difference in the 2D:4D ratio reflects the prenatal influence of androgen on males. A study by Williams, et al. showed that the 2D:4D ratio of homosexual men was not significantly different from that of heterosexual men for either hand.11 However, homosexual women displayed significantly smaller 2D:4D ratios compared with heterosexual women (see figure to right). It has been hypothesized that women exposed to more androgens in the womb tend to express a homosexual orientation. However, since these hormone levels were never measured, one is left with the proxy of finger lengths as a substitute. Studies have found that the more older brothers a boy has, the more likely he is to develop a homosexual orientation.12 This study also found that homosexual men had a greater than expected proportion of brothers among their older siblings (229 brothers: 163 sisters) compared with the general population (106 males: 100 females). Males who had two or more older brothers were found to have lower 2D:4D ratios,11 suggesting that they had experienced increased androgens in the womb. Why increased androgens would predispose both males and females to be homosexual was not explained in the study.

Another study examined the length of long bones in the arms, legs and hands. Both homosexual males and heterosexual females had less long bone growth in the arms, legs and hands, than heterosexual males or homosexual females.13 Accordingly, the researchers hypothesized that male homosexuals had less androgen exposure during development than male heterosexuals, while female homosexuals had greater steroid exposure during development than their heterosexual counterparts. Of course, with regard to male homosexuality, this study directly contradicted the presumed results of the Williams study above, which "showed" that males with multiple older brothers (who tended to be homosexual) experienced increased androgen exposure.

A study of one homosexual vs. two heterosexual male triplets found that the homosexual triplets scored more on the female side of the Masculinity-Femininity scale of the Minnesota Multiphasic Personality Inventory,14 suggesting a possible hormonal influence (decreased androgens) involved in male homosexual orientation.

All of the studies reporting possible hormonal influence on homosexuality suffer from the lack of any real evidence that hormones actually play any role in sexual orientation. The fact that contradictory studies report increased11,15 vs. decreased13-14 androgens as a basis for homosexuality doesn't provoke confidence that the proxies are really true. Obviously, a study that documented real hormone levels, as opposed to proxies, would probably provide more definitive data.

Studies involving a rare hormonal imbalance, congenital adrenal hyperplasia (CAH), caused by defective 21-hydroxylase enzyme, suggest that hormonal abnormalities can influence sexual orientation. CAH results in increased production of male hormones during development. In males, increased androgens has little effect. However, female fetuses that develop in this environment develop ambiguous external genitalia, which complicates subsequent development. In utero treatment with dexamethasone reduces the androgen imbalance, resulting in an individual who is genetically and phenotypically female. However, dexamethasone treatment also results in reduced homosexual orientation among treated females,16 suggesting that some homosexuality may result from hormonal influences during development. Homosexual rights groups have suggested that dexamethasone treatment not be given, because it reduces homosexual orientation in females affected by CAH.

The observation that familial factors influence the prevalence of homosexuality led to a the initiation of number of twin studies, which are a proxy for the presence of possible genetic factors. Most of these early studies suffered from methodological flaws. Kallmann sampled subjects from correctional and psychiatric institutionsnot exactly representative "normal" populations.17 Bailey et al. published a number of studies in the early 1990's, examining familial factors involved in both male and female homosexuality. These studies suffered from the manner in which subjects were recruited, since the investigators advertised in openly gay publications, resulting in skewed populations.18 Later studies by the same group did not suffer from this selection bias, and found the heritability of homosexuality in Australia was up to 50 and 60% in females but only 30% in males.19

A study by Kendler et al. in 2000 examined 1,588 twins selected by a random survey of 50,000 households in the United States.20 The study found 3% of the population consisted of non-heterosexuals (homosexuals and bisexuals) and a genetic concordance rate of 32%, somewhat lower than than found in the Australian studies. The study lost statistical significance when twins were broken down into male and female pairs, because of the low rate (3%) of non-heterosexuals in the general U.S. population.

A Finnish twin study reported the "potential for homosexual response," not just overt homosexual behavior, as having a genetic component.21

On a twist on homosexual twin studies, an Australian research group examined the question of whether homophobia was the result of nature or nurture.22 Surprisingly, both familial/environmental and genetic factors seemed to play a role as to whether or not a person was homophobic. Even more surprising, a separate research group in the U.S. confirmed these results (also adding that attitudes towards abortion were also partly genetic).23 Now, even homophobes can claim that they were born that way!

Twin studies suffer from the problem of trying to distinguish between environmental and genetic factors, since twins tend to live within the same family unit. A study examining the effect of birth order on homosexual preference concluded, "The lack of relationship between the strength of the effect and degree of homosexual feelings in the men and women suggests the influence of birth order on homosexual feelings was not due to a biological, but a social process in the subjects studied."12 So, although the twin studies suggest a possible genetic component for homosexual orientation, the results are certainly not definitive.

An examination of family pedigrees revealed that gay men had more homosexual male relatives through maternal than through paternal lineages, suggesting a linkage to the X chromosome. Dean Hamer24 found such an association at region Xq28. If male sexual orientation was influenced by a gene on Xq28, then gay brothers should share more than 50% of their alleles at this region, whereas their heterosexual brothers should share less than 50% of their alleles. In the absence of such an association, then both types of brothers should display 50% allele sharing. An analysis of 40 pairs of gay brothers and found that they shared 82% of their alleles in the Xq28 region, which was much greater than the 50% allele sharing that would be expected by chance.25 However, a follow-up study by the same research group, using 32 pairs of gay brothers and found only 67% allele sharing, which was much closer to the 50% expected by chance.26 Attempts by Rice et al. to repeat the Hamer study resulted in only 46% allele sharing, insignificantly different from chance, contradicting the Hamer results.27 At the same time, an unpublished study by Alan Sanders (University of Chicago) corroborated the Rice results.28 Ultimately, no gene or gene product from the Xq28 region was ever identified that affected sexual orientation. When Jonathan Marks (an evolutionary biologist) asked Hamer what percentage of homosexuality he thought his results explained, his answer was that he thought it explained 5% of male homosexuality. Marks' response was, "There is no science other than behavioral genetics in which you can leave 97.5% of a phenomenon unexplained and get headlines."29

A study of 13,000 New Zealand adults (age 16+) examined sexual orientation as a function of childhood history.30 The study found a 3-fold higher prevalence of childhood abuse for those who subsequently engaged in same sex sexual activity. However, childhood abuse was not a major factor in homosexuality, since only 15% of homosexuals had experienced abuse as children (compared with 5% among heterosexuals).30 So, it would appear from this population that only a small percentage of homosexuality (~10%) might be explained by early childhood abusive experiences.

If homosexual orientation were completely genetic, one would expect that it would not change over the course of one's life. For females, sexual preference does seem to change over time. A 5-year study of lesbians found that over a quarter of these women relinquished their lesbian/bisexual identities during this period: half reclaimed heterosexual identities and half gave up all identity labels.31 In a survey of young minority women (16-23 years of age), half of the participants changed their sexual identities more than once during the two-year survey period.32 In another study of subjects who were recruited from organizations that serve lesbian/gay/bisexual youths (ages 14 to 21 years) in New York City, the percentage that changed from a lesbian/gay/bisexual orientation to a heterosexual orientation was 5% over the period of just 12 months (the length of the survey).33 Other studies have confirmed that sexual orientation is not fixed in all individuals, but can change over time, especially in women.34 A recent example of an orientation change occurred with The Advocate's "Person of the Year" for 2005. Kerry Pacer was the youngest gay advocate, chosen for her initiation of a "gay-straight alliance" at White County High School in Cleveland, Georgia. However, four years later, she is raising her one year old daughter, along with the baby's father.35 Another former lesbian, British comedienne Jackie Clune, spent 12 years in lesbian relationships before marrying a man and producing 4 children.36 Michael Glatze came out at age 20 and went on to be a leader in the homosexual rights movement. At age 30, he came out in the opposite direction, saying, "In my experience, "coming out" from under the influence of the homosexual mindset was the most liberating, beautiful and astonishing thing I've ever experienced in my entire life."37 A 2011 study of Christian gays who wanted to change their sexual orientation found that 23% of the subjects reported a successful "conversion" to heterosexual orientation and functioning, while an additional 30% reported stable behavioral chastity with substantive dis-identification with homosexual orientation.38 However, 20% of the subjects reported giving up on the process and fully embraced a gay identity, while another 27% fell in between the two extremes.38 Obviously, for at least some individuals, being gay or straight is something they can choose.

The question of nature vs. nurture can also be seen by examining children of homosexual vs. heterosexual parents. If homosexuality were purely biological, one would expect that parenting would not influence it. Paul Cameron published a study in 2006 that claimed that the children of homosexual parents expressed a homosexual orientation much more frequently than the general population.39 Although claims of bias were made against the study, another study by Walter Schuum in 2010 confirmed Cameron's results by statistically examining the results of 10 other studies that addressed the question.40 In total, 262 children raised by homosexual parents were included in the analysis. The results showed that 16-57% of such children adopted a homosexual lifestyle. The results were even more striking in daughters of lesbian mothers, 33% to 57% of whom became lesbians themselves. Since homosexuals makeup only ~5% of the population, it is clear that parenting does influence sexual orientation.

It always amazes me when people say that they were born gay. Looking back on my own experience, I would never say that I was "born straight." I really didn't have any interest in females until about the seventh grade. Before that time, they weren't really interesting, since they weren't interested in sports or riding bikes or anything else I liked to do.

I am not a huge fan of Neo Darwinian evolution. Nevertheless, there is some clear evidence that natural selection (and sexual selection) does act upon populations and has acted on our own species to produce racial differences.41 Natural selection postulates that those genetic mutations that favor survival and reproduction will be selected, whereas those that compromise survival and reproduction will be eliminated. Obviously, a gene or series of genes that produce non-reproducing individuals (i.e., those who express pure homosexual behavior) will be rapidly eliminated from any population. So, it would be expected that any "gay gene" would be efficiently removed from a population. However, it is possible that a gene favoring male homosexuality could "hide" within the human genome if it were located on the X-chromosome, where it could be carried by reproducing females, and not be subject to negative selection by non-reproducing males. In order to survive, the gene(s) would be expected to be associated with higher reproductive capacity in women who carry it (compensating for the generation of non-reproducing males). I can't imagine a genetic scenario in which female homosexuality would ever persist within a population.

Within the last decade, genetic analysis of heritable traits has taken a huge step forward with the advent of DNA microarray technology. Using this technology, it is possible to scan large lengths of the human genome (even an entire genome wide scanGWAS) for numerous individuals, at quite reasonable costs. This DNA microarray technology has led to the discovery of genes that are associated with complex diseases, such as Crohn's Disease, which is the topic of my research. If homosexuality truly has a genetic component, DNA microarray studies would not only definitively prove the point, but would identify specific gene(s) or loci that might be associated with those who express a homosexual orientation. The first attempt to do genome wide scans on homosexual males was done by Mustanski et al. in 2005.42 The results suggested possible linkage near microsatellite D7S798 on chromosome 7q36. However, an attempt to repeat the finding (along with ~6000 well-defined SNPs spread comparatively evenly across the human genome) failed to find any significant SNPs.43 However, a third study using Chinese subjects found a weak association at the SHH rs9333613 polymorphism of 7q36.44 A more general study, examining mate choice among different populations, found no genetic link, prompting the investigators to speculate that such choices were "culturally driven."45 The largest genome wide scan was conducted by 23andMe. 7887 unrelated men and 5570 unrelated women of European ancestry were analyzed by GWAS. Although unpublished, the data was presented at the American Society of Human Genetics annual meeting in San Francisco, showing that there were no loci associated with sexual orientation, including Xq28 on the X chromosome.46 So, the preliminary studies on possible genetic causes of homosexual orientation tends to rule out any dramatic genetic component to sexual orientation.

Why are people gay? The question of how homosexual orientation originates has been the subject of much press, with the general impression being promoted that homosexuality is largely a matter of genes, rather than environmental factors. However, if one examines the scientific literature, one finds that it's not quite as clear as the news bytes would suggest. The early studies that reported differences in the brains of homosexuals were complicated by HIV infection and were not substantiated by larger, better controlled studies. Numerous studies reported that possible hormonal differences affected homosexual orientation. However, these studies were often directly contradictory, and never actually measured any hormone levels, but just used proxies for hormonal influences, without direct evidence that the proxies were actually indicative of true hormone levels or imbalances. Twin studies showed that there likely are genetic influences for homosexuality, although similar studies have shown some genetic influences for homophobia and even opposition to abortion. Early childhood abuse has been associated with homosexuality, but, at most, only explains about 10% of those who express a homosexual orientation. The fact that sexual orientation is not constant for many individuals, but can change over time suggests that at least part of sexual orientation is actually sexual preference. Attempts to find a "gay gene" have never identified any gene or gene product that is actually associated with homosexual orientation, with studies failing to confirm early suggestions of linkage of homosexuality to region Xq28 on the X chromosome. The question of genetic influences on sexual orientation has been recently examined using DNA microarray technology, although, the results have largely failed to pinpoint any specific genes as a factor in sexual orientation.

La Gentica y la Homosexualidad: Nace la gente, homosexual? Last updated November 25, 2013

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Are People Born Gay? Genetics and Homosexuality

Genetics – biology



Homunculus in Sperm One question that has always intrigued us humans is Where did we come from? Long ago, Hippocrates and Aristotle proposed the idea of what they called pangenes, which they thought were tiny pieces of body parts. They thought that pangenes came together to make up the homunculus, a tiny pre-formed human that people thought grew into a baby. In the 1600s, the development of the microscope brought the discovery of eggs and sperm. Antonie van Leeuwenhoek, using a primitive microscope, thought he saw the homunculus curled up in a sperm cell. His followers believed that the homunculus was in the sperm, the father planted his seed, and the mother just incubated and nourished the homunculus so it grew into a baby. On the other hand, Regnier de Graaf and his followers thought that they saw the homunculus in the egg, and the presence of semen just somehow stimulated its growth. In the 1800s, a very novel, radical idea arose: both parents contribute to the new baby, but people (even Darwin, as he proposed his theory) still believed that these contributions were in the form of pangenes.

Modern genetics traces its beginnings to Gregor Mendel, an Austrian monk, who grew peas in a monastery garden. Mendel was unique among biologists of his time because he sought quantifiable data, and actually counted the results of his crosses. He published his findings in 1865, but at that time, people didnt know about mitosis and meiosis, so his conclusions seemed unbelievable, and his work was ignored until it was rediscovered in 1900 by a couple of botanists who were doing research on something else. Peas are an ideal organism for this type of research because they are easy to grow and it is easy to control mating.

We will be looking at the sorts of genetic crosses Mendel did, but first, it is necessary to introduce some terminology:

Monohybrid Cross and Probabilities:

A monohybrid cross is a genetic cross where only one gene/trait is being studied. P stands for the parental generation, while F1 and F2 stand for the first filial generation (the children) and second filial generation (the grandchildren). Each parent can give one chromosome of each pair, therefore one allele for each trait, to the offspring. Thus, when figuring out what kind(s) of gametes an individual can produce, it is necessary to choose one of the two alleles for each gene (which presents no problem if they are the same).

Purple Pea Flower White Pea Flower For example, a true-breeding purple-flowered plant (the dominant allele for this gene) would have the genotype PP, and be able to make gametes with either P or P alleles. A true-breeding white-flowered plant (the recessive allele for this gene) would have the genotype pp, and be able to make gametes with either p or p alleles. Note that both of these parent plants would be homozygous. If one gamete from each of these parents got together to form a new plant, that plant would receive a P allele from one parent and a p allele from the other parent, thus all of the F1 generation will be genotype Pp, they will be heterozygous, and since purple is dominant, they will look purple. What if two individuals from the F1 generation are crossed with each other (PpPp)? Since gametes contain one allele for each gene under consideration, each of these individuals could contribute either a P or a p in his/her gametes. Each of these gametes from each parent could pair with each from the other, thus yielding a number of possible combinations for the offspring. We need a way, then, to predict what the possible offspring might be. Actually, there are two ways of doing this. The first is to do a Punnett square (named after Reginald Crandall Punnett). The possible eggs from the female are listed down the left side, and there is one row for each possible egg. The possible sperm from the male are listed across the top, and there is one column for each possible sperm. The boxes at the intersections of these rows and columns show the possible offspring resulting from that sperm fertilizing that egg. The Punnett square from this cross would look like this:

Note that the chance of having a gamete with a P allele is and the chance of a gamete with a p allele is , so the chance of an egg with P and a sperm with P getting together to form an offspring that is PP is =, just like the probabilities involved tossing coins. Thus, the possible offspring include: PP, ( Pp + pP, which are the same (Pp), since P is dominant over p), so = Pp, and pp.

Another way to calculate this is to use a branching, tree diagram:

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Genetics - biology

Male-pattern hair loss – Wikipedia, the free encyclopedia

Male-pattern hair loss, also known as androgenic alopecia and male pattern baldness (MPB), is hair loss that occurs due to an underlying susceptibility of hair follicles to androgenic miniaturization. It is the most common cause of hair loss and will affect up to 70% of men and 40% of women at some point in their lifetimes. Men typically present with hairline recession at the temples and vertex balding, while women normally thin diffusely over the top of their scalps.[1][2][3] Both genetic and environmental factors play a role, and many etiologies remain unknown.

Classic androgenic hair loss in males begins above the temples and vertex, or calvaria, of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a 'Hippocratic wreath', and rarely progresses to complete baldness.[4] The Hamilton-Norwood scale has been developed to grade androgenic alopecia in males.

Female androgenic alopecia is known colloquially as "female pattern baldness", although its characteristics can also occur in males. It more often causes diffuse thinning without hairline recession; and, like its male counterpart, rarely leads to total hair loss.[5] The Ludwig scale grades severity of androgenic alopecia in females.

Animal models of androgenic alopecia occur naturally and have been developed in transgenic mice;[6]chimpanzees (Pan troglodytes); bald uakaris (Cacajao rubicundus); and stump-tailed macaques (Macaca speciosa and M. arctoides). Of these, macaques have demonstrated the greatest incidence and most prominent degrees of hair loss.[7][8]

Androgenic alopecia is typically experienced as a "moderately stressful condition that diminishes body image satisfaction".[9] However, although most men regard baldness as an unwanted and distressing experience, they usually are able to cope and retain integrity of personality.[10]

Research indicates that the initial programming of pilosebaceous units begins in utero.[11] The physiology is primarily androgenic, with dihydrotestosterone (DHT) the major contributor at the dermal papillae. Below-normal values of sex hormone-binding globulin, follicle-stimulating hormone, testosterone, and epitestosterone are present in men with premature androgenic alopecia compared to normal controls.[12] Although follicles were previously thought permanently gone in areas of complete hair loss, they are more likely dormant, as recent studies have shown the scalp contains the stem cell progenitors from which the follicles arose.[13]

Transgenic studies have shown that growth and dormancy of hair follicles are related to the activity of insulin-like growth factor at the dermal papillae, which is affected by DHT.[14]Androgens are important in male sexual development around birth and at puberty. They regulate sebaceous glands, apocrine hair growth, and libido. With increasing age,[15] androgens stimulate hair growth on the face, but suppress it at the temples and scalp vertex, a condition that has been referred to as the 'androgen paradox'.[16]

These observations have led to study at the level of the mesenchymal dermal papillae.[17][18]Types 1 and 2 5 reductase enzymes are present at pilosebaceous units in papillae of individual hair follicles.[19] They catalyze formation of the androgens testosterone and DHT, which in turn regulate hair growth.[16] Androgens have different effects at different follicles: they stimulate IGF-1 at facial hair, leading to growth, but stimulate TGF 1, TGF 2, dickkopf1, and IL-6 at the scalp, leading to catagenic miniaturization.[16] Hair follicles in anaphase express four different caspases. Tumor necrosis factor inhibits elongation of hair follicles in vitro with abnormal morphology and cell death in the bulb matrix.[20]

Studies of serum levels of IGF-1 show it to be increased with vertex balding.[21][22] Earlier work looking at in vitro administration of IGF had no effect on hair follicles when insulin was present, but when absent, caused follicle growth. The effects on hair of IGF-I were found to be greater than IGF-II.[23] Later work also showed IGF-1 signalling controls the hair growth cycle and differentiation of hair shafts,[14] possibly having an anti-apoptotic effect during the catagen phase.[24]In situ hybridization in adult human skin has shown morphogenic and mitogenic actions of IGF-1.[25] Mutations of the gene encoding IGF-1 result in shortened and morphologically bizarre hair growth and alopecia.[26] IGF-1 is modulated by IGF binding protein, which is produced in the dermal papilla.[27]

DHT inhibits IGF-1 at the dermal papillae.[28] Extracellular histones inhibit hair shaft elongation and promote regression of hair follicles by decreasing IGF and alkaline phosphatase in transgenic mice.[29] Silencing P-cadherin, a hair follicle protein at adherens junctions, decreases IGF-1, and increases TGF beta 2, although neutralizing TGF decreased catagenesis caused by loss of cadherin, suggesting additional molecular targets for therapy. P-cadherin mutants have short, sparse hair.[30]

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Male-pattern hair loss - Wikipedia, the free encyclopedia

Male Hair Loss All You Need To Know – The Belgravia Centre

Although there are a number of hair loss conditions that can affect men, the most common is Male Pattern Baldness (MPB). Other names for this condition are androgenetic alopecia and genetic hair loss. This page will concentrate primarily on this condition but will also make reference to the less widespread hair loss conditions that could be affecting you, with links to more informative pages.

Male Pattern Baldness is a genetic condition that can be passed down from either side of the family tree. So if your Father has a perfectly thick head of hair, dont think you are definitely safe (although you could be!). It is a condition caused by a bi-product of testosterone named Dihydrotestosterone, or DHT. DHT attaches to the hair follicles and causes them to shrink over time, which causes the hair to become thinner and thinner until some men become totally bald on the top of the head.

This is a very good question, and although the answer might seem obvious, many men do not identify their hair loss until it has become fairly advanced, which could be too late to achieve a full recovery. The reasons men do not identify their own hair loss are usually down to simple denial, or because the process is very slow and it is something that they simply might not notice. At the opposite end of the scale, many men worry about hair loss when they have no reason to worry.

The best ways to know if you are losing your hair are:

MPB is in fact easy to identify even for somebody with no clinical experience as it only affects hair on the top of the scalp and not the sides, causing a horseshoe-shaped pattern of hair loss. There are a number of different common patterns of hair loss a receding hairline, a thinning crown, or general thinning spread over the top area of the head. You can read more about these below. MPB never affects the sides or back of the hair.

There are a number of options available for treating Male Pattern Baldness, including clinically proven medications, laser devices and hair restoration surgery. There are also numerous products out there that have no clinical efficacy, so it is easy to waste time and money whilst your hair continues to shed. It is therefore very important that you carry out the necessary research before deciding how you are going to treat your hair loss. The good news is that unless you have lost all or most of your hair, there is a solution out there for you, whether it be a medical solution, a surgical one, or a combination of the two.

Our comprehensive hair loss treatment guide walks you through all the most effective options available for treating hair loss and also gives you an in-depth look at the products that may not be worth using.

hair loss treatment guide

This depends on a number of factors. Firstly, the condition causing your hair loss if you have a temporary hair loss condition (which is unusual in men) then the answer may be no. Please refer to our list of other hair loss conditions below if your problem doesnt appear to be MPB.

Assuming your condition is Male Pattern Baldness, the extent of your eventual hair loss really depends. Those men who have a very early or aggressive onset of MPB are more likely to lose their hair more extensively or at a faster rate, which could result in baldness at an early age. We see men who begin to lose their hair at 18 years old (or sometimes earlier). These men will of course be the ones most likely to reach eventual baldness, sometimes at a fairly early age (mid-twenties). Whereas some men only begin to see signs of thinning in their mid-to-late twenties, or even later. These men are much less likely to experience eventual baldness and may just have thin hair by the time they reach old age.

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Male Hair Loss All You Need To Know - The Belgravia Centre

The Genetics of Male Infertility – The Turek Clinic

Your Expert in Male Fertility & Sexual Health

High technology approaches to fertility, including ICSI, are really a two edged sword: they allow us to treat severe male infertility, but they may alter natural selection in that decisions regarding sperm and eggs are made in the laboratory and not by nature.

Dr. Paul Turek

Among the 15% of couples who experience infertility, about 40% of the time the infertility is due to male factors. About half of male infertility cases are due to defined reasons, including varicocele, infection, hormone imbalances, exposures such as drugs or medications, x-rays, tobacco use and hot tubs, blockage of the reproductive tract ducts, and previous surgery that has left scarring. Another cause of male infertility that has been underestimated in the past, but is now gaining in importance is genetic infertility. The reason for its increased importance is that our knowledge about genetics is growing so quickly. Men who may have had unexplained infertility in the past may now be diagnosed with genetic causes of infertility through recently available testing. In fact, this field is progressing so quickly that genetic infertility has already become one of the most commonly diagnosed reasons for male infertility.

Developed in the early 1990s, assisted reproduction in the form of IVF and ICSI (intracytoplasmic sperm injection) is a revolutionary laboratory technique in which a single sperm is placed directly inside an egg for fertilization. This technique has opened the door to fertility for men who formerly had few available treatment options, as it allows men who were previously considered severely infertile or sterile the possibility of fatherhood. However, with ICSI sperm are chosen by laboratory technicians and not by nature and because of this, it is not clear what barriers to natural selection are altered. Thus, along with this technology comes the possibility of passing on to a child certain genetic issues that may have caused the fathers infertility, or even more severe conditions. Another reason to know whether male

Infertility is genetic or not is because classic treatments such as varicocele repair or medications given to improve male infertility. In fact, Dr Turek was one of the first to publish on this issue, showing that varicocele repair was not effective in improving fertility in men with genetic infertility. Because he recognized these issues early on, Dr. Turek, while at UCSF in 1997, founded the first formal genetic counseling and testing program for infertility in the U.S. Called the Program in the Genetics of Infertility (PROGENI), Dr. Tureks program has helped over 2000 patients at risk for genetic infertility to navigate the decision-making waters that surround this condition.

Men with infertility should be seen by a urologist for a thorough medical history, physical examination, and appropriate medical testing. If genetic infertility is a possibility, then a genetic counselor can help couples understand the possible reasons, offer appropriate genetic testing, and discuss the complex emotional and medical implications of the test results. The approach taken early on by Dr. Turek is outlined in Figure 1. Just like the medical diagnosis from a urologist or fertility specialist, information about family history plays a critical role in genetic risk assessment. This approach to genetic evaluation, termed non-prescriptive, has been the corner- stone of Dr. Tureks critically acclaimed clinical program that now has over a dozen publications contributing to our current knowledge in the field. It is important to note that a lack of family history of infertility or other medical problems does not eliminate or reduce the risk of genetic infertility. In fact, a family history review will often be unremarkable. However, family history can provide crucial supporting in- formation toward making a genetic diagnosis (such as a family history of recurrent miscarriages or babies born with problems). Dr. Turek has published that having a genetic counselor obtain family history information is much more accurate than simply giving patients a written questionnaire to fill out and bring to their visit. A genetic counselor can also discuss appropriate genetic testing options and review the test results in patients in a meaningful way.

When speaking to Dr. Tureks genetic counselor about genetic testing, keep in mind that he or she will not tell you what to do. Genetic counselors are trained to provide information, address questions and concerns, and support you in the decision making process. A genetic counselor does not assume which decisions are most appropriate for you.

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The Genetics of Male Infertility - The Turek Clinic

WHO | Gender and Genetics

Genetic Components of Sex and Gender

Humans are born with 46 chromosomes in 23 pairs. The X and Y chromosomes determine a persons sex. Most women are 46XX and most men are 46XY. Research suggests, however, that in a few births per thousand some individuals will be born with a single sex chromosome (45X or 45Y) (sex monosomies) and some with three or more sex chromosomes (47XXX, 47XYY or 47XXY, etc.) (sex polysomies). In addition, some males are born 46XX due to the translocation of a tiny section of the sex determining region of the Y chromosome. Similarly some females are also born 46XY due to mutations in the Y chromosome. Clearly, there are not only females who are XX and males who are XY, but rather, there is a range of chromosome complements, hormone balances, and phenotypic variations that determine sex.

The biological differences between men and women result from two processes: sex determination and differentiation.(3) The biological process of sex determination controls whether the male or female sexual differentiation pathway will be followed. The process of biological sex differentiation (development of a given sex) involves many genetically regulated, hierarchical developmental steps. More than 95% of the Y chromosome is male-specific (4) and a single copy of the Y chromosome is able to induce testicular differentiation of the embryonic gonad. The Y chromosome acts as a dominant inducer of male phenotype and individuals having four X chromosomes and one Y chromosome (49XXXXY) are phenotypically male. (5) When a Y chromosome is present, early embryonic testes develop around the 10th week of pregnancy. In the absence of both a Y chromosome and the influence of a testis-determining factor (TDF), ovaries develop.

Gender, typically described in terms of masculinity and femininity, is a social construction that varies across different cultures and over time. (6) There are a number of cultures, for example, in which greater gender diversity exists and sex and gender are not always neatly divided along binary lines such as male and female or homosexual and heterosexual. The Berdache in North America, the faafafine (Samoan for the way of a woman) in the Pacific, and the kathoey in Thailand are all examples of different gender categories that differ from the traditional Western division of people into males and females. Further, among certain North American native communities, gender is seen more in terms of a continuum than categories, with special acknowledgement of two-spirited people who encompass both masculine and feminine qualities and characteristics. It is apparent, then, that different cultures have taken different approaches to creating gender distinctions, with more or less recognition of fluidity and complexity of gender.

Sex Chromosome Abnormalities Turner syndrome XXX Females Klinefelter Syndrome XYY Males

Typical sexual development is the result of numerous genes, and mutation in any of these genes can result in partial or complete failure of sex differentiation. These include mutations or structural anomalies of the SRY region on the Y chromosome resulting in XY gonadal dysgenesis, XX males, or XY females; defects of androgen biosynthesis or androgen receptors, and others.

Hermaphroditism Congenital Adrenal Hyperplasia Androgen Insensitivity Syndrome

The issues of gender assignment, gender verification testing, and legal definitions of gender are especially pertinent to a discussion on the ELSI of gender and genetics. These practices, however, are misnomers as they actually refer to biological sex and not gender. Such a discrepancy is highlighted by the existence of intersex individuals whose psychosexual development and gender sometimes do not match the biological sex assigned to them as infants. In this report the term sex will be used where the practice refers to biological sex and not the more social construct of gender.

Gender Assignment of Intersex Infants and Children Legal Definitions of Gender

Chromosomes are the structures that carry genes which in turn transmit hereditary characteristics from parents to offspring. Humans have 23 pairs of chromosomes, one half of each pair inherited from each parent. The Y chromosome is small, carries few genes, and has abundant repetitive sequence, while the X chromosome is more autosome-like in form and content. (14)Despite being relatively gene-poor overall due to reduced recombination, the X and Y sex chromosomes are enriched for genes that relate to sexual development. (15)

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WHO | Gender and Genetics

Male – Wikipedia, the free encyclopedia

A male () organism is the physiological sex that produces sperm. Each spermatozoon can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.

Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically, but in some species it can be determined due to social, environmental or other factors. For example, Cymothoa exigua changes sex depending on the number of females present in the vicinity. [1]

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see Convergent Evolution). The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.[2]

Accordingly, sex is defined operationally across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another.

Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals; male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants.

A common symbol used to represent the male sex is the Mars symbol, (Unicode: U+2642 Alt codes: Alt+11)a circle with an arrow pointing northeast. The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carolus Linnaeus in 1751. The symbol is often called a stylized representation of the Roman god Mars' shield and spear. According to Stearn, however, all the historical evidence favours that it is derived from , the contraction of the Greek name for the planet, Thouros.[3]

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals, such as worms, have both male and female reproductive organs.

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. It is also possible in a variety of species, including human beings, to be XXY or have other intersex/hermaphroditic qualities. These qualities are widely reported to be as common as redheadedness (about 2% of the population).[4] During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female.

The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development;[5] for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development.[6]

The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.[citation needed]

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Male - Wikipedia, the free encyclopedia

Understanding Genetics

-A curious adult from California

August 6, 2004

What a fun question! This sort of thing has been bothering me too lately. The usual statistic is that all people are 99.9% the same. But is that true for men and women?

And what about our similarity to other animals? We are really only about 80% the same as a mouse at the genetic level so men and women are clearly more similar to each other than to mice. But what about chimpanzees? If people really are 98.7% the same as a chimpanzee, are male chimpanzees closer genetically to men than men are to women?

As you know, men have an X and a Y chromosome and women have two X chromosomes. So besides the usual 0.1% (or 3.2 million base pair) difference between people, men and women differ by the presence of the Y chromosome.

The Y chromosome is a tiny thing; it is about 59 million base pairs long and has only 78 genes. If we look at base pairs, the difference between men and women would be 59 million divided by 3.2 billion or about 1.8%. This translates to men and women being 98.2% the same.

Men and women are actually a bit more similar as the Y chromosome has about 5% of its DNA sequences in common with the X chromosome. This would change the number to 98.4% the same.

If the 98.7% number for chimp-human similarity is right, then by this measure, men and women are less alike than are female chimps and women. (More recent data suggests that chimps may be 95% instead of 98.7% the same, but this is still up in the air.)

Now if we look at the gene level instead of at the base pair level, men and women become much more similar. If we assume 30,000 total genes, then men and women are about 99.7% the same instead of 98.4%. (I haven't been able to find a good number for how many genes chimpanzees and humans share.)

So is the bottom line that men and male chimps have more in common than men and women? Of course not. If we take a closer look, we see some of the dangers of looking at raw percentages instead of individual changes.

Understanding Genetics

URNotAlone Profile for Lynda Flores, Genetic Male Straight …

Member Type: Silver Member Age: 39 Location: Mexico City Juarez, Mexico Orientation: Straight (Genetic Male ) Listed As: Girl (M2F) Looking For: Friends, Genetic Female (GG), Girls (MtoF) Last Active: May 20th, 2015 Joined: Jul 18th, 2007 About Me

Hello everyone!

It is proven that having too much information in your profile is not an effective way to meet people LOL.

So I think that now I would rather say: "Please ask if you want to know".

I consider myself a big fan of everything feminine, and in a certain way I feel empathic towards anyone who shares this passion with me.

I'm not into kinky stuff such as having cybersex, sex-cams, phone, etc. Of course I prefer to talk with people that have complete profiles but I do understand why some people needs to remain anonymous.

Please check out my Facebook profile. I will add you if you happen to have a complete profile too 😉



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URNotAlone Profile for Lynda Flores, Genetic Male Straight ...

Androgenic alopecia – Wikipedia, the free encyclopedia

Androgenic alopecia (also known as androgenetic alopecia, alopecia androgenetica, or male pattern baldness) is hair loss that occurs due to an underlying susceptibility of hair follicles to androgenic miniaturization. It is the most common cause of hair loss and will affect up to 70% of men and 40% of women at some point in their lifetimes. Men typically present with hairline recession at the temples and vertex balding, while women normally thin diffusely over the top of their scalps.[1][2][3] Both genetic and environmental factors play a role, and many etiologies remain unknown.

Classic androgenic hair loss in males begins above the temples and vertex, or calvaria, of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a 'Hippocratic wreath', and rarely progresses to complete baldness.[4] The Hamilton-Norwood scale has been developed to grade androgenic alopecia in males.

Female androgenic alopecia is known colloquially as "female pattern baldness", although its characteristics can also occur in males. It more often causes diffuse thinning without hairline recession; and, like its male counterpart, rarely leads to total hair loss.[5] The Ludwig scale grades severity of androgenic alopecia in females.

Animal models of androgenic alopecia occur naturally and have been developed in transgenic mice;[6]chimpanzees (Pan troglodytes); bald uakaris (Cacajao rubicundus); and stump-tailed macaques (Macaca speciosa and M. arctoides). Of these, macaques have demonstrated the greatest incidence and most prominent degrees of hair loss.[7][8]

Research indicates that the initial programming of pilosebaceous units begins in utero.[9] The physiology is primarily androgenic, with dihydrotestosterone (DHT) the major contributor at the dermal papillae. Below-normal values of sex hormone-binding globulin , follicle-stimulating hormone , testosterone, and epitestosterone are present in men with premature androgenic alopecia compared to normal controls.[10] Although follicles were previously thought permanently gone in areas of complete hair loss, they are more likely dormant, as recent studies have shown the scalp contains the stem cell progenitors from which the follicles arose.[11]

Transgenic studies have shown that growth and dormancy of hair follicles are related to the activity of insulin-like growth factor at the dermal papillae, which is affected by DHT.[12]Androgens are important in male sexual development around birth and at puberty. They regulate sebaceous glands, apocrine hair growth, and libido. With increasing age,[13] androgens stimulate hair growth on the face, but suppress it at the temples and scalp vertex, a condition that has been referred to as the 'androgen paradox'.[14]

These observations have led to study at the level of the mesenchymal dermal papillae.[15][16]Types 1 and 2 5 reductase enzymes are present at pilosebaceous units in papillae of individual hair follicles.[17] They catalyze formation of the androgens testosterone and DHT, which in turn regulate hair growth.[14] Androgens have different effects at different follicles: they stimulate IGF-1 at facial hair, leading to growth, but stimulate TGF 1, TGF 2, dickkopf1, and IL-6 at the scalp, leading to catagenic miniaturization.[14] Hair follicles in anaphase express four different caspases. Tumor necrosis factor inhibits elongation of hair follicles in vitro with abnormal morphology and cell death in the bulb matrix.[18]

Studies of serum levels of IGF-1 show it to be increased with vertex balding.[19][20] Earlier work looking at in vitro administration of IGF had no effect on hair follicles when insulin was present, but when absent, caused follicle growth. The effects on hair of IGF-I were found to be greater than IGF-II.[21] Later work also showed IGF-1 signalling controls the hair growth cycle and differentiation of hair shafts,[12] possibly having an anti-apoptotic effect during the catagen phase.[22]In situ hybridization in adult human skin has shown morphogenic and mitogenic actions of IGF-1.[23] Mutations of the gene encoding IGF-1 result in shortened and morphologically bizarre hair growth and alopecia.[24] IGF-1 is modulated by IGF binding protein, which is produced in the dermal papilla.[25]

DHT inhibits IGF-1 at the dermal papillae.[26] Extracellular histones inhibit hair shaft elongation and promote regression of hair follicles by decreasing IGF and alkaline phosphatase in transgenic mice.[27] Silencing P-cadherin, a hair follicle protein at adherens junctions, decreases IGF-1, and increases TGF beta 2, although neutralizing TGF decreased catagenesis caused by loss of cadherin, suggesting additional molecular targets for therapy. P-cadherin mutants have short, sparse hair.[28]

At the occipital scalp, androgens enhance inducible nitric oxide synthase (iNOS), which catalyzes production of nitric oxide from L-arginine.[14] The induction of iNOS usually occurs in an oxidative environment, where the high levels of nitric oxide produced interact with superoxide, leading to peroxynitrite formation and cell toxicity. iNOS has been suggested to play a role in host immunity by participating in antimicrobial and antitumor activities as part of the oxidative burst[29] of macrophages.[30] The gene coding for nitric oxide synthase is on human chromosome 17.[31]

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Androgenic alopecia - Wikipedia, the free encyclopedia

Difference Between Male and Female BirdsGenetics and …

Sex-Linked Traits in Bird Genetics

Understanding the ZZ/ZW sex chromosome system is important for people who breed birds, whether the interest is in chicken genetics, parrot genetics, or some other type of bird. The way sex-linked traits are inherited is opposite to the way they are inherited by humans and other mammals.

For example, in cockatiels, budgerigars (parakeets), lovebirds, and other small parrots, the lutino color mutation is a sex-linked recessive trait. Lutino birds lack the dark pigment melanin, which is responsible for black, gray, and blue coloration in birds. As a result, lutino birds appear to have significant yellow coloration, which would ordinarily be covered up by melanin.

The lutino gene is located on the Z chromosome. Since lutino females have only one Z chromosome, they will pass this chromosome down to all their sons (remember male birds are ZZ), but not to their daughters (female birds are ZW and get the Z chromosome from their fathers).

A male bird will be lutino only if his father has the gene and his mother has the mutation as well. With a non-lutino mother, a male that inherits lutino from his father will be a heterozygous carrier, but will not have a lutino phenotype. A lutino-colored male must be homozygous, since the trait is recessive. In this situation all his daughters will be lutino-colored and all his sons will be carriers.

For a non-lutino carrier male (heterozygous), each daughter has a 50% chance of being lutino, and each son has a 50% chance of being a carrier.

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Difference Between Male and Female BirdsGenetics and ...

Male Infertility | Genetic Abnormalities or Male …

The development of in vitro fertilitzation (IVF) has allowed many couples to have the families they might otherwise have been unable to create independently. At the same time, this technology has allowed researchers to study the genetic make-up of the earliest stages of embryos. These advances are providing insights into the link between genetics and infertility and how defects (mutations) in specific genes may result in male or female infertility.It is possible that many cases of unexplained infertility will one day be found to have a clear genetic basis.

What has been learned in the last two decades of assisted reproduction is that some cases of severe male factor infertility are clearly related to gene deletions, mutations or chromosomal abnormalities.

Some men with very severe male factor infertility will be found, upon testing their blood chromosomes (known as a karyotype) to have an extra X chromosome. That is, instead of having a 46 XY karyotype, they have a 47 XXY karyotype. This condition is known as Klinefelter Syndrome and can result in failure to achieve puberty or even when puberty is achieved, these men often have male infertility. Some men with Klinefelter Syndrome can father pregnancies through the use of in vitro fertilitzation (IVF) with Intra-Cytoplasmic Sperm injection (ICSI).So far, we are not seeing an increased risk of Klinefelter Syndrome or other chromosome abnormalities in the offspring achieved in these cases.

Also discovered in recent years is that some men with very severe low sperm counts will be found to have deletions in a certain part of their Y chromosome, known as the DAZ gene. Their karyotype is normal (46 XY) but close inspection of the Y chromosome shows there are sections of the chromosome that are missing. A portion of these men will have no recoverable sperm in the ejaculate or on testicular surgery and donor sperm is the only option. With other deletions in the DAZ gene, there is a small amount of sperm present and conception with IVF-ICSI is possible. In these cases, the male offspring which will always inherit their fathers Y chromosome, will also have this deletion, and will themselves be infertile.

A single gene mutation in the gene for Cystic Fibrosis (CF) is associated with absence of the part of the tube (the vas deferens) that leads from the testicle to the urethra in the penis. These men are usually carriers for the CF gene mutation and do not themselves have the disease of Cystic Fibrosis. Sperm can be recovered from the testicles in these men to be used for IVF with ICSI but it is imperative that their wife (or egg provider) be fully tested for CF mutations as well, otherwise there is significant risk of having a child with Cystic Fibrosis.

For men with sperm counts routinely in the less than 5 million total motile sperm range, testing for genetic conditions is warranted so that these men or couples can be made aware of the genetic issues and how these issues might affect their offspring.

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Male Infertility | Genetic Abnormalities or Male ...

Male infertility – Wikipedia, the free encyclopedia

Male infertility refers to a male's inability to cause pregnancy in a fertile female. In humans it accounts for 40-50% of infertility.[1][2][3] It affects approximately 7% of all men.[4] Male infertility is commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.[5]

Factors relating to male infertility include:[6]

Pre-testicular factors refer to conditions that impede adequate support of the testes and include situations of poor hormonal support and poor general health including:

Male smokers also have approximately 30% higher odds of infertility.[9][not in citation given] There is increasing evidence that the harmful products of tobacco smoking kill sperm cells.[10][11] Therefore, some governments require manufacturers to put warnings on packets. Smoking tobacco increases intake of cadmium, because the tobacco plant absorbs the metal. Cadmium, being chemically similar to zinc, may replace zinc in the DNA polymerase, which plays a critical role in sperm production. Zinc replaced by cadmium in DNA polymerase can be particularly damaging to the testes.[12]

Common inherited variants in genes that encode enzymes employed in DNA mismatch repair are associated with increased risk of sperm DNA damage and male infertility.[13] As men age there is a consistent decline in semen quality, and this decline appears to be due to DNA damage.[14] (Silva et al., 2012). These findings suggest that DNA damage is an important factor in male infertility.

Testicular factors refer to conditions where the testes produce semen of low quantity and/or poor quality despite adequate hormonal support and include:

Radiation therapy to a testis decreases its function, but infertility can efficiently be avoided by avoiding radiation to both testes.[20]

Post-testicular factors decrease male fertility due to conditions that affect the male genital system after testicular sperm production and include defects of the genital tract as well as problems in ejaculation:

The diagnosis of infertility begins with a medical history and physical exam by a physician or nurse practitioner. Typically two separate semen analyses will be required. The provider may order blood tests to look for hormone imbalances, medical conditions, or genetic issues.

The history should include prior testicular or penile insults (torsion, cryptorchidism, trauma), infections (mumps orchitis, epididymitis), environmental factors, excessive heat, radiation, medications, and drug use (anabolic steroids, alcohol, smoking).

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Male infertility - Wikipedia, the free encyclopedia

Size Genetics – Male Enhancement Reviews

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Size Genetics - Male Enhancement Reviews

HitXP Science of Genetics behind the Hindu Gotra System …

This article is merely an attempt to find the scientific reasoning behind the origins of the ancient Gotra System and in no way endorses its imposition in the modern Hindu society to decide marriages or other things. In all probabilities, the modern Gotra system is no more relevant, and the best method to verify the genetic feasibility of a marriage, if at all required, would be to avoid cousin marriages (which have been proved to increase the risk of genetic disorders in the off springs) or to do a genetic test of the bride and grooms DNA for any possible genetic disorders in their off springs.

The Gotra is a system which associates a person with his most ancient or root ancestor in an unbroken male lineage. For instance if a person says that he belongs to the Bharadwaja Gotra then it means that he traces back his male ancestry to the ancient Rishi (Saint or Seer) Bharadwaja. So Gotra refers to the Root Person in a persons male lineage.

The Gotra system is practiced amongst most Hindus. See here for a List of Hindu Gotras practiced by different sections of the Hindu Society

Brahmins identify their male lineage by considering themselves to be the descendants of the 8 great Rishis ie Saptarshis (The Seven Sacred Saints) + Bharadwaja Rishi. So the list of root Brahmin Gotras is as follows

These 8 Rishis are called Gotrakarin meaning roots of Gotras. All other Brahmin Gotras evolved from one of the above Gotras. What this means is that the descendants of these Rishis over time started their own Gotras. The total number of established Gotras today is 49. However each of them finally trace back to one of the root Gotrakarin Rishi.

The word Gotra is formed from the two Sanskrit words Gau (meaning Cow) and Trahi (meaning Shed). Note that the English word Cow is a derived word of the Sanskrit word Gau with the same meaning Gau.

So Gotra means Cowshed, where in the context is that Gotra is like the Cowshed protecting a particular male lineage. Cows are extremely important sacred animals to Hindus and there were a large number of best breeds of Cows that ancient Hindus reared and worshipped, and hence the name Gotra referring to the system of maintaining individual male lineages seems more appropriate.

This Gotra system helps one identify his male lineage and is passed down automatically from Father to Son. But the Gotra system does not get automatically passed down from Father to Daughter. Suppose a person with Gotra Angirasa has a Son. Now suppose the Son gets married to a girl whose father belongs to Gotra Kashyapa. The Gotra of the girl automatically is said to become Angirasa after her marriage even though her father belonged to Gotra Kashyapa.

So the rule of the Gotra system is that the Gotra of men remains the same, while the Gotra of the woman becomes the Gotra of their husband after marriage. Now suppose a person has only daughters and no sons. In that case his Gotra will end with him in that lineage because his daughters will belong to the Gotras of their husbands after their marriage!

This was probably the reason why in the ancient vedic or hindu societies it was preferred to have atleast one Son along with any number of daughters, so that the Gotra of the father could continue.

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HitXP Science of Genetics behind the Hindu Gotra System ...