Why does the recombination frequency of genes vary with the distance between them in the chromosome?
The farther the distance among the loci of two genes in a chromosome the higher the recombination frequency between these genes. This is true as once alleles are nearer in the chromosome it is more probable that they are kept united when chromosomal extremities are exchanged by crossing over. Alternatively, if they are farther apart it will be easier for them to separate by crossing over.