Centimorgan. In genetics, a centimorgan (abbreviated cM) or map unit (m.u.) is a unit for measuringgenetic linkage. It is defined as thedistance between chromosomepositions (also termed loci or markers) for which the expected average number of intervening chromosomalcrossovers in a single generation is 0.01.
One map unit (m.u) is equivalent to one % recombinant genotypes.