A gene is a short piece of DNA. Genes tells the body how to build a specific proteins. There are about 30,000 genes in each cell of the human body. Together, these genes make up the blueprint for the human body and how it works.
A person's genetic makeup is called a genotype.
Genes are made of DNA. Strands of DNA strands make up part of your chromosomes. Chromosomes have matching pairs of one copy of a specific gene. The gene occurs in the same position on each chromosome.
Genetic traits, such as eye color, are dominant or recessive:
Dominant traits are controlled by one gene in the pair of chromosomes.
Recessive traits need both genes in the gene pair to work together.
Many personal characteristics, such as height, are determined by more than one gene. However, some diseases, such as sickle cell anemia, can be caused by a change in a single gene.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.