1. Why is crossing over between two genes on the same chromosome from 0% to 50%, and not higher? 2. Why is linkage between two genes on the same chromosome from 50% to 100%, and not lower? Solution They are so far apart on one chromosome that there is a 100% likelihood of a crossover occurring between them - 50% recombination frequency because only half the chromatids are involved in a crossover event (except rare cases) Because crossing over occurs at the 4-strand stage of the cell cycle (that is, after S phase) so that each single crossover involves only 2 of the 4 chromatids. So 50% parental chromatids are produced and 50% crossover chromatids are produced. Genetic linkage: genes located on same chromosome may be inherited together in genetic crosses.