Genetics Review

NCBI Home NCBI Site Map      brief/complete Course Description Schedule Introduction Genetics Review Types of Databases Format of Sequence Record Entrez BLAST 3-D Structures Genomes and Maps Librarian Roles WWW Sites Glossaries and Dictionaries

Genetic Map Source:  image from the Cooperative Human Linkage Center (CHLC), CHLC Marker Maps. Definition A genetic map, also known as a linkage map, is a chromosome map of a species that shows the position of its known genes and/or markers relative to each other, rather than as specific physical points on each chromosome. One tool used in creating genetic linkage maps is a pedigree -- a simplified diagram of a family's genealogy that shows family members' relationships to each other and how a particular trait or disease has been inherited. Source:  definition from the National Human Genome Research Institute (NHGRI) Glossary of Genetic Terms. More... Scale:  centiMorgans (cM) A centiMorgan is a unit of genetic distance that represents a 1% probability of recombination during meiosis. E.g., if two genes are 1 cM apart, there is a 1% chance they will break apart during meiosis. If two genes are 20 cM apart, there is a 20% chance they will break apart during meiosis. One cM is equivalent, on average, to a physical distance of approximately 1 megabase in the human genome. This is just an average because genetic recombination rates vary along different parts of the chromosomes.

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Revised September 29, 1999 Comments/questions about course to Renata Geer renata@ncbi.nlm.nih.gov Questions about NCBI resources to info@ncbi.nlm.nih.gov