Question

The phenotype of vestigial (short) wings (vg) in Drosophila melanogaster is caused by a recessive mutant gene that independently assorts with a recessive gene for hairy (h) body. Assume that a cross is made between a fly the is homozygous for normal wings with a hairy body and a fly with vestigial wings that is homozygous for normal body hair. The wild-type F1 flies were crossed among each other to produce 1024 offspring. Which phenotypes would you expect among the 1024 offspring, and how many of each phenotype would you expect?

Answer 1

576 wild type, 192 hairy body, 192 vestigial wings and 64 vestigial wings, hairy body

Step-by-step explanation:

In Drosophila, vestigial wings (vg) is caused by a recessive mutation to the dominant wild type wings (vg+).

A different, independent gene has a recessive allele (h) that can cause hairy body and a dominant wild type body (h+).

A cross is made between a fly that is homozygous for normal wings with a hairy body (vg+vg+ hh) and a fly with vestigial wings that is homozygous for normal body hair (vgvg h+h+).

All the F1 flies will be heterozygous for both genes vg+vg hh+, with wild-type phenotype.

A cross F1 x F1 was made that produced 1024 offspring. This is a dihybrid cross, so following Mendel's law of independent assortment the expected phenotypic proportions in the offspring will be 9:3:3:1. Among 1024 offspring, the expected number of individuals with each phenotype will be:

vg+_h+_ : 9/16 × 1024 = 576 wild type

vg+_ hh : 3/16 × 1024 = 192 hairy body

vgvg h+ : 3/16 × 1024 = 192 vestigial wings

vgvg hh : 1/16 × 1024 = 64 vestigial wings, hairy body