Genetic Map

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.

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.