Chapter 13, Problem 27P

In Drosophila, the wild-type red eye color is produced by the X-linked allele ${\text{w}}^{\text{+}}$ Mutants for eye color often lack the ability to deposit pigment in the eye and have whiteeye color. For the purpose of this problem, assume thatin Southern blot analysis a molecular probe hybridizes toa $\text{5-kb}$ fragment of DNA from the eye-color locus. Theprobe binds to DNA fragments containing either wild-typeor mutant sequence.

If a male Drosophilahas white eye color as a result of inactivation of ${\text{w}}^{\text{+}}$ by movement of a $\text{3-kb}$ Pelement into the wild-type allele, diagram the expectedSouthern blot pattern of DNA fragments from wild type males and white-eyed males and females that carry the mutant allele. Explain your reasoning.

Several male progeny of a female carrier of the mutantallele have red sectors on their eyes. The number andsize of the sectors vary among the males. Explain theorigin of these red sectors, and account for the variationin number and size.

If Southern blotting is used to compare DNA isolatedfrom a white sector and a red sector of the same eye, is a difference in DNA fragment size expected? Explain.