"A unit used to express distances on a genetic map. In genetic mapping, distances between markers are determined by measuring the rate of meoitic recombination between them, which increases proportionately with the distance separating them. A cM is defined as the length of an interval in which there is a 1% probability of recombination. On the average, 1 cM is roughly equivalent to 1 megabase (Mb) of DNA, although this can vary widely due to hot and cold spots of recombination." [NCBI:http\://www.ncbi.nlm.nih.gov/SCIENCE96/Glossary.html]