Why are genetic and physical distances different between males and females and different for parts of a chromosome?
Physical distance between two linked loci can be estimated from genetic distance using the following relationship: 1 centiMorgan = 1 megabase pair (1 x 10^6 base pairs). This relationship assumes that all regions of a chromosome have an equal probability of recombination events. While this is often the case, some very important exceptions exist. Centromeres exert crossover suppression. This effect causes recombination events in the region of the centromere to occur at a much, much lower frequency than expected. Due to crossover suppression, two loci located near a centromere will behave as if they were very closely linked even though they might be physically far away from each other. The pseudoautosomal region (PAR), located near the p termini of both the X and Y chromosomes, allows for the homologous pairing of the X and Y chromosomes during meiosis I in males. In males, a chiasmata always forms in the pseudoautosomal region during meiosis I. If the genetic distances between two marke
