A gene is the part of a body cell that contains genetic material or
deoxyribonucleic acid (DNA), which determines a person's physical traits.
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.
Many genes together make up chromosomes. Defects in genes or
chromosomes may cause changes in certain body processes or functions. These
changes may be undetectable or may cause genetic diseases, such as hemophilia
or Down syndrome. Some conditions, such as juvenile rheumatoid arthritis and
depression, may also be affected by genetic problems.
Defective genes can be passed from parents to children. Diseases
that run in families are often caused by genetic defects. A person may be born
with a certain genetic makeup that makes him or her susceptible or at risk for
a certain condition.
