Printer Friendly VersionEmail A FriendAdd ThisIncrease Text SizeDecrease Text Size




A gene is a short piece of DNA, which tells the body how to build a specific protein. There are approximately 30,000 genes in each cell of the human body. The combination of all genes makes up the blueprint for the human body and its functions.

A person's genetic makeup is called a genotype.


Genes are located on strands of DNA, just like beads on a string. The DNA strands make up the chromosomes.

Chromosomes contain matching pairs of one copy of a specific gene. The gene occurs in the same position on each chromosome.

In females, one sex chromosome gets its gene from the mother, the other matching sex chromosome has the gene from the father.

In males, a single X chromosome comes from the mother and a non-matching Y chromosome comes from the father.

Genetic traits, such as eye color, are described as dominant or recessive:

  • Dominant traits are controlled by one gene in the pair.
  • Recessive traits require both genes in the gene pair to work together to control the trait.

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. For detailed information, see heredity and disease.

See also:

Review Date: 2/20/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission ( URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- 2009 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

Home Page
Why Choose Us
Website Terms of Use

Visitor & Patient Info
Patient Portal
We Speak Your Language
Patient Privacy
Contact Us

Find a Physician
Medical Services
Maimonides In the News
Directions & Parking

Medical Education
Career Opportunities
Nurses & Physicians
Staff Intranet Access
Maimonides Medical Center    |    4802 Tenth Avenue    |    Brooklyn, NY 11219    |    718.283.6000    |