Question

2. Black bodies and vestigial wings in Drosophila are caused by recessive alleles on chromosome 2. A long-winged male with yellow-brown body color, homozygous for the wild-type alleles, b+b+ v+v+, was exposed to X-rays to induce mutations in germ-line cells (i.e. to generate mutations in the gametes the male produced). He was then mated to a homozygous recessive black-bodied, vestigial-winged female, bb vv. Among the offspring, a male with a black body and vestigial wings was observed.

a. What are the expected genotypes and phenotypes of the progeny of the cross given above?

b. Describe a chromosomal rearrangement that would explain the observed black-bodied, vestigial-winged male.

Answer 1

These are autosomal recessive traits.

b+b+ v+v+= A long winged male with yellow-brown body color.

bb vv= A vestigial winged female with black body.

Male b+b+ v+v+ was exposed to Xrays which cause mutations in their germ cells. So gametes genyotype was changed.

Cross per formed between mutaed male with bbvv female

b+b+ v+v+ (Mutated)X bbvv gives bbvv offspring.

Normally from b+b+ v+v+, b+v+ gametes is formed.

Similarly from bbvv, bv gamete is formed.

From thie we expect all progenies are b+b v+v genotype, means all are Yellow brown with long wings. But surprisingly bbvv genotye also observed. This is due to mutation of male. This mutant change the germinal cells.

a) b+b v+v X bbvv

?

?

F1: 1 b+b v+v: 1b+b vv:1 bb v+v: 1 bbvv genotypic ratio

1 Yellow long: 1 Yellow vestigial: 1 black long: 1 black vestigial.

b)