This Article  • Full text  • PDF  • Send to a friend  • Save in My Folder  • Save to citation manager  • Permissions  Citing Articles  • Contact me when this article is cited  Related Content  • Similar articles in JAMA  Topic Collections  • Genetics, Other  • JAMA Patient Page  • Alert me on articles by topic

	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

Genetics includes the study of how human characteristics are inherited from one's parents. It explains how traits as simple as eye color or as complex as susceptibility to diseases run in families. Genes are units of heredity passed from parents to offspring and are contained in a person's cells—every human cell contains about 20 000 to 25000 genes. Genes vary greatly from person to person and influence personality, intelligence, physical appearance, and other traits to a certain extent, but learning and environment play important roles as well. The March 19, 2008, issue of JAMA is a theme issue on genetics. This Patient Page is adapted from one published in the November 14, 2001, issue of JAMA.

GENETICS TERMINOLOGY

• DNA (deoxyribonucleic acid) is the chemical inside a gene that carries genetic instructions for making living things. DNA is made of 2 long, twisting molecules called the double helix.
  
• Chromosomes are packets of . . . [Full Text of this Article]