Map Distance can be
defined as the expression of the probability that crossing over will occur
between two genes (loci) and it is measured as a Centimorgan (cM).
1 Centimorgan or 1 map unit is equivalent to 1% crossing
over. So if recombinant frequency between genes Dand B is 32%, the distance
between them is 32 map units or 32 cM.