Centimorgan

In genetics, a centimorgan (abbreviated cM) or map unit (m.u.) is a unit of recombinant frequency for measuring genetic linkage. It is often used to imply distance along a chromosome. The number of base-pairs it corresponds to varies widely across the genome (different regions of a chromosome have different propensities towards crossover). One centimorgan corresponds to about 1 million base pairs in humans on average^{[1] [2]}. The centimorgan is equal to a 1% chance that a marker at one genetic locus on a chromosome will be separated from a marker at a second locus due to crossing over in a single generation. Plasmodium falciparum has an average recombination distance of ~15 kb per centimorgan: markers separated by 15 kb of DNA (15,000 nucleotides) have a 1% chance of being separated by crossing over in a single generation. Note that non-syntenic genes are inherently unlinked, and cM distances have no meaning between them.

The centimorgan was named in honor of geneticist Thomas Hunt Morgan by his student Alfred Henry Sturtevant. Note that the parent unit of the centimorgan, the morgan, is rarely used today.

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