A centiMorgan (cM) is a measurement of how likely a segment of DNA is to recombine from one generation to the next. A single centiMorgan is considered equivalent to a 1% (1/100) chance that a segment of DNA will crossover or recombine within one generation.

For humans, one million base pairs (bp) average about one centiMorgan. However, the rate of recombination is highly variable.