Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb,48 Aabb,52 aaBb,94 aabb.These results are consistent with the following circumstance:
A) sex-linked inheritance with 30% crossing over.
B) linkage with 50% crossing over.
C) linkage with approximately 33 map units between the two gene loci.
D) independent assortment.
E) 100% recombination.

Question

Quizplus · Accepted Answer

The results of the cross are not consistent with independent assortment, as the number of each phenotype indicates that the two genes are linked. The numbers of each phenotype also do not match those that would be expected if the genes were sex-linked with 30% crossing over or if there was 100% recombination.

The most likely explanation is that the genes are linked with approximately 33 map units between them. This is because the numbers of each phenotype are consistent with a 1:1:1:1 ratio for a dihybrid cross with linked genes, and a map distance of 33 map units corresponds to a 1:1:1:1 ratio of offspring. This indicates that approximately one-third of the offspring should be recombinant for the two genes. Therefore, choice C is the best choice.

Assume That a Cross Is Made Between AaBb and Aabb