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Genetics


Topic Overview

What are genes?

Genes are the part of a body cell that contain 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 problems 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.

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. These 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 for 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 show 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 show that you have an increased risk for developing a disease such as breast cancer, you may make decisions that help lower your risk of breast cancer.
  • You may feel reassured if the tests are normal.

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

Genetic testing can be used to find out the identity of a child's father (paternity). It can also be used in crime scene investigation.

What are the main types of genetic testing?

There are six main types of genetic testing:

  • Carrier identificationClick here to see an illustration. determines whether people who have a family history of a specific disease or who are in a group that has an increased chance for that disease are likely to pass on that disease to their children. Information obtained from this type of testing can help guide a couple as they make decisions about pregnancy.
  • Prenatal testing determines whether a fetus has a disorder, such as Down syndrome. Information gained from this type of testing can help guide decisions about how to manage a pregnancy, including the decision about whether to end the pregnancy.
  • Newborn screening checks for various metabolic diseases, such as phenylketonuria (PKU). Information obtained from newborn screening can help guide medical treatment to ensure the best possible outcome for the baby.
  • Late-onset disease testing determines whether you carry a genetic change that increases your risk for developing a disease, such as breast cancer or Huntington's disease, later in life. This might be of interest if you have a relative who has the disease. Information from this type of testing can help you make decisions about preventing or managing the disease.
  • Genetic identification (DNA fingerprinting) can be used to determine paternity, help solve crimes, and identify a body. DNA fingerprinting is more accurate than dental records, blood type, or traditional fingerprints.
  • Compatibility testing looks at genetic markers to see if an organ for transplant is suitable for a person who needs it.

What are the risks of genetic testing?

Information from genetic testing can affect your life and the lives of your family members. The issues involved include:

  • Psychological. The emotions you may experience if you learn that you have a greater chance of having or passing on a serious disease can cause you to feel anxious or depressed. This may also affect your relationship with your partner or other family members. Genetic counseling is recommended prior to genetic testing.
  • Medical. A person who tests positive for a disease-specific gene may decide to use preventive or treatment options to reduce the impact or severity of the disease. Although many treatment options are proved effective, others may be potentially dangerous or of unproven value.
  • Privacy. Because genetic testing is expensive, few people are able to afford it without help from their insurance companies. Many people worry that genetic information released to insurance companies may affect future employment options or insurance availability. The discovery of a genetic disease that is not causing symptoms now (such as breast cancer or Huntington's disease) should not affect your future ability to gain employment or health insurance coverage. A law in the United States, called the Genetic Information Nondiscrimination Act of 2008 (GINA), protects people who have DNA differences that may affect their health. This law does not cover life insurance, disability insurance, or long-term care insurance.
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