Morgan (unit)

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In genetics, a centimorgan (abbreviated cM) is a unit of recombinant frequency for measuring genetic linkage. It is often used to imply distance along a chromosome. 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. A 50 cM distance means that the genes will reassort when an odd number of crossings happen, which happens 31.8% of the time. Note that non-syntenic genes are inherently unlinked, and cM distances have no meaning.

Another unit of recombination frequency is the map unit (m.u.) with one m.u. equaling a recombination frequency of 1%. A map unit is synonymous with centimorgan.

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.

In humans, a centiMorgan corresponds roughly to a megabase of DNA sequence.