Chapter 12, Problem 5P

One of the X chromosomes in a particular Drosophila female had a normal order of genes but carried recessive alleles of the genes for yellow body color (y), vermilion eye color (v), and forked bristles (f), as well as the dominant X-linked Bar eye mutation (B). Her other X chromosome carried the wild-type alleles of all four genes, but the region including y⁺, v⁺, and f⁺ (but not B⁺) was inverted with respect to the normal order of genes. This female was crossed to a wild-type male as diagrammed here.

The cross produced the following male offspring:

a.	Why are there no male offspring with the allele combinations y v f+, y+ v+ f, y v+ f+, or y+ v f (regardless of the allele of the Bar gene)?
b.	What kinds of crossovers produced the y v f B+ and y+ v+ f+ B offspring? Can you determine any genetic distances from these classes of progeny?
c.	What kinds of crossovers produced the y+ v f+ B+ and y v+ f B offspring?