Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate, Inc. and/or its affiliates. All Rights Reserved.

Genetics: Glossary of terms

Benjamin A Raby, MD, MPH
Robert D Blank, MD, PhD
Section Editor
Anne Slavotinek, MBBS, PhD
Deputy Editor
Jennifer S Tirnauer, MD


One of the greatest obstacles clinicians experience in reading about and understanding genetics is the extensive use of technical language and jargon. It should be noted that genetic terms are frequently used imprecisely in published clinical literature. The following is a compilation of some of the most important technical terms.

A more extensive discussion of terms can be accessed in standard genetics reference texts [1]. In addition, a guide for the conventions regarding the proper names of genes and alleles in humans can be found at www.genenames.org/guidelines.html.

Glossaries of epidemiological terms and terms that apply to systematic reviews and meta-analyses are presented separately in UpToDate. (See "Glossary of common biostatistical and epidemiological terms" and "Systematic review and meta-analysis", section on 'Glossary of terms'.)


Allele — An allele is one of a series of alternative forms (genotypes) at locus, or a specific region of a chromosome. At the DNA level, different alleles have different base sequences.

Allelic fraction — The allelic fraction can be defined as the number of times a mutated base is observed, divided by the total number of times any base is observed at the locus [2]. Allelic fraction is generally applied to a single mutation in a tumor, and thus is distinct from allelic frequency, which examines the frequency of an allele in a population (see 'Allele frequency' below). Mutation fraction can be defined as the ratio between mutant and wild-type alleles in a tumor sample.

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:

Subscribers log in here

Literature review current through: Nov 2017. | This topic last updated: Aug 02, 2017.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.
Topic Outline