What are genes?

Genes are the part of a body cell that contains the biological information that parents pass to their children. Genes control the growth and development of cells. Genes are contained in DNA (deoxyribonucleic acid), a substance inside the center (nucleus) of cells that contains instructions for the development of the cell.

You inherit half of your genetic information from your mother and the other half from your father. Genes, alone or in combination, determine what features (genetic traits) a person inherits from his or her parents, such as blood type, hair color, eye color, and other characteristics, including risks of developing certain diseases. Certain changes in genes or chromosomes may cause defects in various body processes or functions.

What are chromosomes?

Many genes together make up larger structures within the cell called chromosomes. Each cell normally contains 23 pairs of chromosomes.¹

A human has 46 chromosomes (23 pairs). One chromosome from each pair comes from the mother, and one chromosome from each pair comes from the father. One of the 23 pairs determines your sex. The sex chromosomes are called X and Y.

• For a child to be female, she must inherit an X chromosome from each parent (XX).
• For a child to be male, he must inherit an X chromosome from his mother and a Y chromosome from his father (XY).

Some genetic disorders are caused when all or part of a chromosome is missing, or when an extra chromosome or chromosome fragment is present.

What is genetic testing?

Genetic testing examines a DNA sample for gene changes, or it may analyze the number, arrangement, and characteristics of the chromosomes. Testing may be performed on samples of blood, semen, urine, saliva, stool, body tissues, bone, or hair.

Should I have genetic testing?

You may choose to have genetic testing if you are concerned that you have an increased risk of having or getting a disease that has a genetic cause. The information you obtain from the tests may help you make decisions about your life. For example:

• If tests determine that you have an increased risk for passing on a disease to your child, you may choose to have more genetic testing while you are pregnant (prenatal testing). Or you may decide to adopt a child.
• If tests determine that you have an increased risk for developing a disease such as breast cancer, you may make decisions that help lower your risk for breast cancer.
• You may feel reassured if the tests are normal.

You may decide to have a genetic test during pregnancy to determine whether your fetus has a disorder, such as Down syndrome. Information obtained from the test can help you decide how to manage your pregnancy.