In Drosophila melanogaster,vestigial wings are caused by a recessive allele of a gene that is linked to a gene with a recessive allele that causes black body color.Morgan crossed black-bodied normal-winged females and gray-bodied vestigial-winged males.The F₁ were all gray bodied,normal winged.After examining the F₂ progeny,Morgan calculated the map distance to be 17 map units.Which of the following is correct about the F₂ progeny?

Question

Quizplus · Accepted Answer

The map distance of 17 units indicates that the two genes (one for body color and one for wing shape) are about 17 map units apart on the same chromosome. This means that crossing over between the two genes occurs about 17% of the time. Therefore, the 17% refers to the frequency of recombination (crossing over) between the two genes, not the frequency of each phenotype. According to the cross given, the F₂ progeny would have included four phenotypes: black-bodied, normal-winged (BBWW), gray-bodied, normal-winged (BbWw or bbWw), gray-bodied, vestigial-winged (Bbww or bbww), and black-bodied, vestigial-winged (BBww). The only answer choice that includes the correct phenotypes is C, which states that the gray-bodied, normal-winged flies and the black-bodied, vestigial-winged flies occur at a frequency of 17%.

In Drosophila Melanogaster,vestigial Wings Are Caused by a Recessive Allele