Chapter 13, Problem 30P

Flies homozygous for mutant alleles of a Drosophila gene called rough have slightly malformed (rough) eyes, instead of normal smooth eyes. Two different strains of flies exist, each with a different P element-induced mutant rough allele. In each strain, the P element in the rough gene is the only P element in the fly genome.

a.	When homozygotes for one of the rough mutant alleles were bred for several generations, in each generation flies appeared either with wild-type eyes, or with much more severely rough eyes. Pure-breeding wild-type or severely rough-eyed lines could be generated from these unusual flies. Explain.
b.	When homozygotes for the other rough mutant allele were grown for many generations, neither wild-type flies nor flies with more severely rough eyes were ever seen. Explain.