A dihybrid in cis is crossed to a dihybrid in trans (the two genes of interest,A and B,are linked).What proportion of the progeny is expected to be homozygous recessive with respect to the two genes of interest?
A)less than 6.25%
B)more than 6.25%,but less than 18.75%
C)about 18.75%
D)more than 18.75%,but less than 37.5%
E)more than 37.5%

Question

Quizplus · Accepted Answer

In a dihybrid cross involving linked genes, the proportion of progeny that are homozygous recessive for both genes is expected to be less than what would be predicted by independent assortment due to linkage. Since the genes are linked, recombinant types (which would include the double homozygous recessive type) are less common than parental types. The percentage given in choice A, less than 6.25%, reflects the reduced likelihood of obtaining a homozygous recessive individual for both traits due to this linkage, as 6.25% would be the expected proportion for each trait being homozygous recessive if the genes were assorting independently (1/16). With linkage, the actual proportion is even lower, especially in the absence of significant crossing over between the genes.

A Dihybrid in Cis Is Crossed to a Dihybrid in Trans