Question

When two genes are linked but quite far apart, their estimated map distance, based on recombination frequencies, is often an underestimation of their true map distance. what is the explanation for this underestimation?

Answer 1

This underestimation is due to the possible crossovers, double or multiple, that may lead to a parental arrangement of alleles so that the products of the meiosis aren't taken into account when measuring recombinant frequency.