Drosophila (fruit flies) usually have long wings, but mutations in the BT gene can result in bent wings and mutations in the VG gene can result in vestigial wings. If flies that are heterozygous for both the bent wing gene and the vestigial wing gene are mated, what is the probability of offspring with bent wings only? Note that the mutant alleles of both genes are recessive.

Explanation:

1. As given;

Normal drosophila  have long wings;

BT gene mutated  drosophila  have bent wings;

VG gene mutated  drosophila  have vestigial wings.

Mutant alleles of both genes are recessive.

2. Cross between heterogyzous flies for both the bent and  vestigial wing genes = +bt +vg  and +bt +vg  heterozygotes;

3. Progeny;   From these parents, the probability of offspring with bent wings( recessive )= 3/16.  

So, 3 offspring out of 16 have bent wings.