Question

In Morgan's testcross of a gray-bodied, long-winged heterozygous female Drosophila with a homozygous recessive black-bodied, vestigial-winged male, the following offspring were obtained: 965 gray body, long wing; 944 black body, vestigial wing; 206 gray body, vestigial wing; 185 black body, long wing. Focusing only on the recombinant classes (gray body, vestigial wing and black body, long wing), the numbers of offspring of each type are similar (206 and 185). What accounts for the similar number of offspring of each recombinant phenotype?

Answer 1

The similar number of offspring of each recombinant phenotype occurs as a result of Crossing over between chromosomes that are reciprocal, such that when a recombinant chromosome of one type is formed, the opposite recombinant of that same type is also formed.