Have people ever said to you, "It's in your genes"? They were probably talking about a physical characteristic, personality trait, or talent that you share with other members of your family.

We know that genes play an important role in shaping how we look and act and even whether we get sick. Now scientists are trying to use that knowledge in exciting new ways, such as treating health problems.

To understand how genes work, let's review some biology basics. Most living organisms are made up of cells that contain a substance called deoxyribonucleic (pronounced: dee-AHK-see-rye-bow-noo-KLEE-ik) acid (DNA).

DNA contains four chemicals (adenine, thymine, cytosine, and guanine called A, T, C, and G for short) that are strung in patterns on extremely thin, coiled strands in the cell. How thin? Cells are tiny invisible to the naked eye and each cell in your body contains about 6 feet of DNA thread, for a total of about 3 billion miles of DNA inside you!

So where do genes come in? Genes are made of DNA, and different patterns of A, T, G, and C code for the instructions for making things your body needs to function (like the enzymes to digest food or the pigment that gives your eyes their color). As your cells duplicate, they pass this genetic information to the new cells.

DNA is wrapped together to form structures called chromosomes. Most cells in the human body have 23 pairs of chromosomes, making a total of 46. Individual sperm and egg cells, however, have just 23 unpaired chromosomes. You received half of your chromosomes from your mother's egg and the other half from your father's sperm cell. A male child receives an X chromosome from his mother and a Y chromosome from his father; females get an X chromosome from each parent.

Genes are sections or segments of DNA that are carried on the chromosomes and determine specific human characteristics, such as height or hair color. Because you have a pair of each chromosome, you have two copies of every gene (except for some of the genes on the X and Y chromosomes in boys, because boys have only one of each).

Some characteristics come from a single gene, whereas others come from gene combinations. Because every person has about 25,000 different genes, there is an almost endless number of possible combinations!

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The Basics on Genes and Genetic Disorders

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