Chapter 13, Problem 8P

A series of chromosomal mutations in Drosophila were used to map the javelin gene, which affects bristle shape, and the henna gene, which affects eye pigmentation. Both the javelin and the henna mutant alleles are recessive to wild type. The chromosomal mutations are all rearrangements of chromosome 3. A diagram of chromosome 3 follows: 3L is the left arm, and 3R is the right arm. The DNA sequences are numbered from bp #1 to bp #24, 598, 654 on 3L, and bp #1 to bp #27, 929, 329 on 3R.

The chromosomal breakpoints for six chromosome 3 rearrangements are indicated in the following table. The exact breakpoints of each chromosomal mutation have been determined using PCR and DNA sequencing. For example, deletion A has one breakpoint just after bp #6, 000, 587, and another just after bp #6, 902, 063 on the left arm of chromosome 3.

Flies with a chromosome containing one of these six rearrangements (deletions or inversions) were mated to flies homozygous for both javelin and henna. The phenotypes of the heterozygous progeny (that is, rearrangement/javelin, henna) are shown here.

a.	Using these data, what can you conclude about the locations of the javelin and henna genes on chromosome 3?
b.	For each chromosome rearrangement, draw on a diagram of a normal chromosome 3 the positions and 5′-to-3′ orientations of PCR primer pairs that could be used to amplify an approximately 100 bp region containing the rearrangement breakpoints.