Sex-Linked Inheritance Problem Set

Sex-Linked Inheritance Problem Set 2

Problem 3 Tutorial: A fly cross involving two X-linked traits

What offspring would you expect from a cross between the female Drosophila described in problem 1 (red eyes and a yellow body, homozygous recessive for the yellow body color allele and homozygous dominant for the eye color allele) and the male described in problem 2 (hemizygous for both the recessive (white) eye color allele and dominant (tan) body color allele?)

A reminder that the alleles for eye color and for body color are on the X chromosome of Drosophila, but not on the Y. Red eye color (w+) is dominant to white eye color (w), and tan body color (y+) is dominant to yellow body color (y).

Genotypes and phenotypes of parents

The yellow-bodied, red-eyed female is homozygous for the dominant red-eye color and for the recessive yellow-body color.

The tan-bodied, white-eyed male is hemizygous for both the recessive white-eye color and the dominant tan-body color.

Genotypes and phenotypes of offspring (F1)

The daughters inherit a dominant red-eye allele from the mother and a dominant tan-body allele from the father. They are heterozygous for both eye and body color.

Since the alleles for eye color and for body color are on the X chromosome of Drosophila, the sons inherit these traits from the mother only. Their phenotype is the same as that of the mother.

The Biology Project
University of Arizona
Tuesday, August 13, 1996
lapointe@u.arizona.edu