Archive for the ‘Female Genetics’ Category

Structural abnormalities where there is a problem with the structure of a chromosome Examples include translocations, duplications and deletions of part of a chromosome

Aneuploid eggs and embryos are also responsible for most of the decline in overall fertility with female aging - and for the low pregnancy success rates with IVF for women over 40.

The increased rate of chromosomal abnormalities in women of advanced reproductive age has been well documented in research studies. The graph below shows the rate of chromosomally abnormal IVF eggs by female age. These numbers are approximate and compiled from several studies.

We do not know exactly why there is an increase in chromosomal abnormalities in the eggs of women as they age. However, research studies have clarified some of the issues involved.

The meiotic spindle is a critical component of eggs that is involved in organizing the chromosome pairs so that a proper division of the pairs can occur as the egg is developing. An abnormal spindle can predispose to development of chromosomally abnormal eggs.

An excellent study published in the medical journal "Human Reproduction" in October of 1996 investigated the influence of maternal age on meiotic spindle assembly in human eggs.

The pictures below are from this journal article. These photos were taken with confocal fluorescence microscopy of eggs stained with special dyes to show the spindles and chromosomes.

When the chromosomes line up properly in a straight line on the spindle apparatus in the egg, the division process would be expected to proceed normally so that the egg would end up with its proper complement of 23 chromosomes.

However, with a disordered arrangement on an abnormal spindle, the division process may be uneven - resulting in an unbalanced chromosomal situation in the egg.

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Female Age and Chromosome Problems in Eggs and Embryos

Curious to know what determines the gender of a baby?

The mystery lies in the chromosomes. The knowledge of chromosomes is essential for understanding human genetics. The field has attracted much research and everyday there are ongoing discoveries. Human cells consist of 46 chromosomes which make 23 pairs. In males and females, the first 22 are similar across both genders and are known as autosomes. The last one pair (23rd) is known as the sex chromosome and makes all the difference.

The sex chromosome of females contains two Xs while that for males contains one Y and one X. The presence of this last chromosome pair determines the gender of a baby. Apart from the X and Y difference, these chromosomes have many other differences which form the characteristics of the two genders. Knowing these differences is going to help you understand the differences between the genetic make up of the two genders and pave way for more research.

The behaviour of this X chromosome in males is different from those in the female chromosome.

The female chromosome has more working genes than the male one. It is known to have more than 1000 working genes while the male chromosome has less than 100. Of these 1000 working genes, 200 to 300 are gender specific while the remaining are shared across the two genders.

Average female chromosomes are recorded to be greater in size than male chromosome. Exceptions may occur but these are the average measurements. The specific cause for this is not known yet.

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Female Chromosome:

The female sex chromosome pair does not contain any Y chromosome. The pair is an XX and the two X chromosomes are equal in size and chromosomal pairing.

An additional X chromosome, giving an XXX configuration, results in triple X syndrome where a women is taller than others and has an average IQ. If there is just one X in the sex chromosome, the Turners syndrome occurs where a born female is shorter, infertile and lower in IQ level than those with normal XX pairs.

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Difference between Male and Female Chromosomes

Scientists have found genetic evidence for what some men have long suspected: it is dangerous to make assumptions about women. The key is the X chromosome, the "female" sex chromosome that all men and women have in common. In a study published this week in the journal Nature, scientists said they had found an unexpectedly large genetic variation in the way parts of womens two X chromosomes are distributed among them. The findings were published in conjunction with the first comprehensive decoding of the chromosome. Females can differ from each other almost as much as they do from males in the way many genes at the heart of sexual identity behave, researchers say. "Literally every one of the females we looked at had a different genetic story," says Duke University genetics expert Huntington Willard, who co-wrote the study. "It is not just a little bit of variation." The analysis also found that the obsessively debated differences between men and women were, at least on the genetic level, even greater than previously thought. As many as 300 of the genes on the X chromosomes may be activated differently in women than in men, says the other author of the paper, Laura Carrel, molecular biologist at the Pennsylvania State University College of Medicine. The newly discovered genetic variation between women might help account for differing gender reactions to prescription drugs and the heightened vulnerability of women to some diseases, experts say. "The important question becomes how men and women actually vary and how much variability there is in females," Carrel says. "We now might have new candidate genes that could explain differences between men and women." All told, men and women may differ by as much as 2 per cent of their entire genetic inheritance, greater than the hereditary gap between humankind and its closest relative, the chimpanzee. "In essence," Willard says, "there is not one human genome, but two: male and female." SCIENTISTS estimate that there may be as many as 30,000 genes in the chemical DNA blueprint for human growth and development known as the human genome. The genes are parcelled in 23 pairs of rod-like structures called chromosomes, which are contained in every cell of the body. The most distinctive of the chromosomes are the mismatched pair of X and Y chromosomes that guide sexual development. Until now, researchers considered the shuffle of sex chromosomes at conception a simple matter of genetic roulette. The chromosomes that dictate sexual development are mixed and matched in predictable combinations: A female inherits one X chromosome from each parent; a male inherits an X chromosome from his mother and a Y chromosome from his father. To avoid any toxic effect from double sets of X genes, female cells randomly choose one copy of the X chromosome and "silence" it - or so scientists had believed. The new analysis found that the second X chromosome was not a silent partner. As many as 25 per cent of its genes are active, serving as blueprints to make necessary proteins. To investigate this variation, Carrel and Willard isolated cells from 40 women and measured the activity of hundreds of genes to see whether those on the second X chromosome were active or silent. Although those extra genes were supposed to be turned off, they found that about 15 per cent of them in all female cells were still active, or "expressed". In some women, up to an additional 10 per cent of those X-linked genes showed varying patterns of activity. "This is 200 to 300 genes that are expressed up to twice as much as in a male or some other females," Willard says. "This is a huge number." Researchers were surprised that they found so many unexpected differences in the behaviour of the one sex chromosome that men and women share. Though there is dramatic variation in the activation of genes on the X chromosomes that women inherit, there is none among those in men, the researchers reported. Researchers have yet to understand the effect of so many different patterns of gene activation among women, or determine what controls them, but all the evidence suggests that they are not random. ILLUMINATING this complex palette was the work of an international team of 250 scientists, led by geneticist Mark Ross, at the Wellcome Trust Sanger Institute in Hinxton, Cambridge. The team produced the first complete sequence of the X chromosome about two years after the decoding of the male Y chromosome. The researchers found that the X chromosome, though relatively poor in genes, is rich in influence, deceptively subtle, and occasionally deadly to males. The international team identified 1,098 functional genes along the X chromosome, more than 14 times as many as scientists had located on the tiny Y chromosome. Even so, the researchers say, there are fewer genes to be found on the X chromosome than on any of the other 22 chromosomes sequenced so far. Most of the X genes are slightly smaller than average. But one is the largest known gene in the human genome, a segment of DNA linked to diseases such as muscular dystrophy, that is more than 2.2 million characters long. The X chromosome contains a larger share of genes linked to disease than any other chromosome. It is implicated in 300 hereditary disorders, including colour blindness, haemophilia and Duchenne muscular dystrophy. Nearly 10 per cent of the genes may belong to a group known to be more active in testicular cancers, melanomas and other cancers, the team reports. "The biggest surprise for us was just how many of these [cancer-related] genes there are on the X," Ross says. The complete gene sequence provided some clues to the origins of the human sex chromosomes. The researchers found that most of the genes on the X chromosome also reside on chromosome 1 and chromosome 4 of chickens. That supports the theory that the human sex chromosomes evolved from a regular pair of chromosomes from a common ancestor of chickens and humans - about 300 million years ago. 2005 Scotsman.com http://news.scotsman.com/scitech.cfm?id=295472005

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Galaxy Of Genetic Differences Between Men & Women

Karyotype of a normal male with 22 pairs of autosomes and one pair of sex chromosomes. U.S. Department of Energy Human Genome Program

How Chromosomes Determine Sex:

Chromosomes are long, stringy aggregates of genes that carry heredity information. They are composed of DNA and proteins and are located within the nucleus of our cells. Chromosomes determine everything from hair color and eye color to sex. Whether you are a male or female depends on the presence or absence of certain chromosomes.

Human cells contain 23 pairs of chromosomes for a total of 46.

There are 22 pairs of autosomes and one pair of sex chromosomes. The sex chromosomes are the X chromosome and the Y chromosome.

Sex Chromosomes:

In human sexual reproduction, two distinct gametes fuse to form a zygote. Gametes are reproductive cells produced by a type of cell division called meiosis. Gametes are also called sex cells. They contain only one set of chromosomes and are said to be haploid.

The male gamete, called the spermatozoan, is relatively motile and usually has a flagellum. The female gamete, called the ovum, is nonmotile and relatively large in comparison to the male gamete. When the haploid male and female gametes unite in a process called fertilization, they form what is called a zygote. The zygote is diploid, meaning that it contains two sets of chromosomes.

Sex Chromosomes X-Y:

The male gametes or sperm cells in humans and other mammals are heterogametic and contain one of two types of sex chromosomes. They are either X or Y. The female gametes or eggs however, contain only the X sex chromosome and are homogametic.

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How Chromosomes Determine Sex - About

Reviewed January 2012

The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The X chromosome spans about 155 million DNA building blocks (base pairs) and represents approximately 5 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in cells other than egg cells. This phenomenon is called X-inactivation or Lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.

Some genes on the X chromosome escape X-inactivation. Many of these genes are located at the ends of each arm of the X chromosome in areas known as the pseudoautosomal regions. Although many genes are unique to the X chromosome, genes in the 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.

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 X chromosome likely contains 800 to 900 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

Genes on the X 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 X chromosome. This list of disorders associated with genes on the X 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 X 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.

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 in adolescent and adult males. Extra copies of genes from the pseudoautosomal regions 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.

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X chromosome - Genetics Home Reference

Prospects for improving female fertility in dairy cattle via genetic selection are reviewed. Today's high-producing cows have shorter estrous cycles, fewer standing events, shorter duration of estrus, and more frequent multiple ovulations. Although high milk production is often implicated as the cause of impaired fertility, the impact of inadequate body condition appears to be greater, as the latter has a significant impact on probability of conception, rate of embryonic loss, and proportion of anestrous animals. Genetic improvement of female fertility can be achieved by indirect selection for productive life (PL) or body condition score (BCS), or by direct selection for traits such as daughter pregnancy rate (DPR). Most leading dairy countries have implemented genetic evaluation systems for female fertility in the past decade, but refinement of these systems to account for hormonal synchronization, differences in the voluntary waiting period, exposure to natural service bulls, and other confounding factors is warranted. Recent work has focused on the development of data collection and genetic evaluation systems that will allow selection of bulls that have daughters that are resistant to common health disorders, including mastitis, lameness, ketosis, displaced abomasum, and metritis. Such systems will allow selection of animals that can remain healthy and fertile while producing large quantities of milk.

The challenges associated with achieving pregnancy in modern, high-producing dairy cows have received considerable attention from scientists, veterinarians, and farmers in recent years. Todays dairy cows tend to have lower conception rate, greater days open, and greater likelihood of culling due to infertility than their counterparts from two or three decades ago. Genetic selection programs have led to rapid gains in milk yield and conformation traits; but performance for traits such as female fertility, longevity, and susceptibility to disease has tended to decline. While it is impossible to completely disentangle the effects of selection from simultaneous changes in nutrition, cow care, and reproductive management, it is clear that geneticists failed to pay adequate attention to health, fertility, and longevity traits until the past decade. The magnitude of genetic variation in such traits is surprising, and we are now poised to take advantage of recent research and development efforts regarding the definition, measurement, and genetic analysis of these traits.

The objective of this paper is to review the relationships between female fertility and other economically important dairy traits and to discuss opportunities for improving reproductive performance through direct selection of highly fertile animals or indirect selection of animals that maintain adequate body condition and resist metabolic and infectious diseases during lactation.

Please check this link first if you are interested in organic or specialty dairy production

Milk production of dairy cows on modern commercial farms has roughly doubled over the past four decades. First parity cows on large commercial dairy farms typically peak at 40 to 45 kg/d, while second and later parity cows typically peak at 50 to 55 kg/d. Furthermore, each group typically sustains daily milk production of 40 kg/d or more during the first seven months postpartum. Therefore, one might expect differences in the reproduction of high-producing cows, as compared with low-producing cows or yearling heifers.

Lopez et al. (2005) discussed some of the differences between the reproductive biology of lactating Holstein cows and yearling Holstein heifers. In particular, Lopez et al. (2005) noted that lactating cows have shorter duration of estrus (7 to 8 hr vs. 11 to 14 hr), longer and more variable estrous cycles (20 to 29 d vs. 20 to 23 d), larger diameter of ovulatory follicles (16 to18 mm vs. 14 to 16 mm), and greater rates of anovulation (20 to 30% vs. 1 to 2%), multiple ovulation (20 to 25% vs. 1 to 3%), and pregnancy loss (20 to 30% vs. 3 to 5%).

Lopez et al. (2005) also documented differences in these characteristics between lactating cows according to levels of milk production. They (Lopez et al., 2005) used the HeatWatch system (DDx Inc., Denver, Colorado) to monitor the estrous characteristics of 146 high-producing Holstein cows (46.4 kg/d for the 10 d preceding estrus) and 177 low-producing Holstein cows (33.5 kg/d for the 10 d preceding estrus). High-producing cows had shorter duration of estrus (6.2 hr vs. 10.9 hr), fewer standing events (6.3 vs. 8.8), and shorter standing time per event (21.7 sec vs. 28.2 sec). Duration of estrus decreased linearly from 14.7 hr for cows milking 25 to 30 kg/d to 2.8 hr for cows milking 50 to 55 kg/d. In addition, the percentage of cows with multiple ovulations increased from 0.0% for cows milking between 25 and 30 kg/d to 51.6% for cows between 50 and 55 kg/d.

The rate of early embryonic loss in Holstein cows is also a major concern, as noted in several recent studies that have used ultrasound for pregnancy detection at 27 to 31 d after breeding, followed by pregnancy confirmation via rectal palpation at 39 to 48 d after breeding. Reported rates of embryonic loss during this interval ranged from 0.70 to 1.40% per day (e.g., Cartmill et al., 2001; Cerri et al., 2004; Santos et al., 2004). However, estimates of the rate of embryonic loss (particularly those from commercial farms) may be biased upward by false positive diagnoses at the early ultrasound exam, as most veterinarians tend to use caution when declaring cows as non-pregnant in herds that use hormonal resynchronization programs.

On large western dairy farms, mean veterinary-confirmed conception rates of Holstein cows at 75 d after breeding were nearly constant over the first five inseminations (0.30, 0.31, 0.31, 0.29, and 0.28, respectively), while means for Jersey cows declined linearly from the first through fifth insemination (0.42, 0.38, 0.34, 0.29, and 0.27, respectively). Mean conception rate at first service tended to decline with age in both breeds (0.35, 0.29, 0.28, 0.26, and 0.25, respectively, for first through fifth parity Holsteins and 0.44, 0.43, 0.41, 0.39, and 0.37, respectively, for first through fifth parity Jerseys), though the rate of decline was less noticeable for repeat inseminations than for first insemination (Weigel, 2006 (unpublished)). Both breeds have been selected for many generations under similar management conditions, and both have made rapid genetic progress over the past three decades (mean mature equivalent 305 d milk yield increased from 6,904 to 11,608 kg in Holsteins and from 4,461 kg to 8,273 kg in Jerseys from 1970 to 2000). Differences in mean conception rate within the Holstein breed were found among cows at different levels of daily milk yield, but such differences were smaller than one might expect (Weigel, 2005 (unpublished)). Mean conception rates at 75 d after breeding were 0.33, 0.33, and 0.32 for primiparous Holstein cows that averaged < 27 kg/d, 27 to 36 kg/d, and > 36 kg/d, respectively, during the first 3 mo of lactation; whereas corresponding means were 0.28, 0.28, and 0.27 for multiparous Holstein cows that averaged < 36 kg/d, 36 to 45 kg/d, and > 45 kg/d, respectively. In Wisconsin Holsteins, Lopez et al. (2005) found no relationship between the percentage of cows exhibiting anovulatory condition and level of daily milk yield. The percentage of anovular cows was 27.8% for cows that were milking 25 to 30 kg/d and 26.3% for cows that were milking 50 to 55 kg/d (means for 5-kg intervals in between ranged from 21.7% to 35.1%, with no apparent trend). In California Holsteins, Santos et al. (2004) found a weak, nonsignificant relationship between milk yield and rate of embryonic loss between 31 and 45 d after breeding, with rates of 9.7% for cows that were milking 36 kg/d and 12.7% for cows that were milking 52 kg/d. Thus, it does not appear that increased milk yield is solely responsible for the decline in mean reproductive performance.

High milk production, whether achieved through genetic selection, enhanced nutrition, or improved management, is often implicated as the cause of health, fertility, and culling problems on modern dairy farms. However, a complex relationship exists between milk yield, health, and reproductive performance. High-producing cows tend to be more susceptible to metabolic disorders and infectious diseases, and these can lead to impaired fertility. On the other hand, healthy cows tend to have higher milk production and greater reproductive performance than unhealthy cows. Conversely, cows that remain nonpregnant for much of the lactation tend to achieve higher levels of total production because fewer resources are allocated to the developing calf. Thus, one must be cautious when attempting to formulate cause-effect relationships between these traits.

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Impact of Genetic Selection on Female Fertility - eXtension

Female () is the sex of an organism, or a part of an organism, that produces non-mobile ova (egg cells). Most female mammals, including female humans, have two X chromosomes.

The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male. A female individual cannot reproduce sexually without access to the gametes of a male (an exception is parthenogenesis). Some organisms can reproduce both sexually and asexually.

There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages.[citation needed] Patterns of sexual reproduction include

Other than the defining difference in the type of gamete produced, differences between males and females in one lineage cannot always be predicted by differences in another. The concept is not limited to animals; egg cells are produced by chytrids, diatoms, water moulds and land plants, among others. In land plants, female and male designate not only the egg- and sperm-producing organisms and structures, but also the structures of the sporophytes that give rise to male and female plants.

The word female comes from the Latin femella, the diminutive form of femina, meaning "woman". It is not etymologically related to the word male, but in the late 14th century the spelling was altered in English to parallel the spelling of male.[2]

A distinguishing characteristic of the class Mammalia is the presence of mammary glands. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are most obvious in humans, as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Mammary glands are present in all mammals, although they are vestigial in the male of the species.

Most mammalian females have two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome (but some mammals, such as the Platypus, have different combinations). To compensate for the difference in size, one of the female's X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactived in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can also give rise to other combinations, but this usually results in sterility.

Mammalian females bear live young (with the rare exception of monotremes, which lay eggs). Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as sharks, whose eggs hatch inside their bodies, also have the appearance of bearing live young.

A common symbol used to represent the female sex is (Unicode: U+2640 Alt codes: Alt+12), a circle with a small cross underneath. According to Schott,[3] the most established view is that the male and female symbols "are derived from contractions in Greek script of the Greek names of these planets, namely Thouros (Mars) and Phosphoros (Venus). These derivations have been traced by Renkama[4] who illustrated how Greek letters can be transformed into the graphic male and female symbols still recognised today." Thouros was abbreviated by , and Phosphoros by , which were contracted into the modern symbols.

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 have both male and female reproductive organs.

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Female - Wikipedia, the free encyclopedia

The human female reproductive system (or female genital system) contains two main parts: the uterus, which hosts the developing fetus, produces vaginal and uterine secretions, and passes the male's sperm through to the fallopian tubes; and the ovaries, which produce the female's egg cells. These parts are internal; the vagina meets the external organs at the vulva, which includes the labia, clitoris and urethra. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the ovaries release an ovum, which passes through the Fallopian tube into the uterus. If, in this transit, it meets with sperm, the sperm penetrate and merge with the egg, fertilizing it.

During the reproductive process, the egg releases certain molecules that are essential to guiding the sperm and these allow the surface of the egg to attach to the sperm's surface then the egg can absorb the sperm and fertilization begins. The fertilization usually occurs in the oviducts, but can happen in the uterus itself. The zygote then implants itself in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis. When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the fetus through the birth canal, which is the vagina.

The ova are larger than sperm and have formed by the time a female is born. Approximately every month, a process of oogenesis matures one ovum to be sent down the Fallopian tube attached to its ovary in anticipation of fertilization. If not fertilized, this egg is flushed out of the system through menstruation.

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Definition Of female reproductive system |Genetic ...