what is the relationship between the degree of crossing over and the distance between two genes?

The relationship between the degree of crossing over and the distance between two genes is direct: the greater the distance between two genes on a chromosome, the higher the frequency or degree of crossing over between them. This is because crossovers are more likely to occur in the larger physical space between genes during meiosis. Consequently, the frequency of crossovers is proportional to the distance separating the genes, and this principle is used in genetic mapping to estimate gene distances as map units or centimorgans. Thus, crossing over frequency serves as a measure of the relative distance between genes—farther apart genes show more recombination due to higher crossing over probability.