Sex-Linked Inheritance Problem Set
Problem 1: Crossing a white-eyed female and red-eyed male fly
Tutorial to help answer the question
In a cross between a white-eyed female fruit fly and red-eyed male, what percent of the female offspring will have white eyes? (White eyes are X-linked, recessive.)
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Tutorial
Genotypes and phenotypes of parents
The female parent must be homozygous because she has the recessive white-eyed phonotype.
The male parent is hemizygous, red-eyed.
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Genotypes and phenotypes of offspring
All of the females eggs will contain an X chromosome with the white-eye mutation.
The sperm will contain either a normal X chromosome or a Y chromosome.
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Summary
We use a Punnett Square to predict the outcome of this cross Female offspring receive an X chromosome from both the sperm and egg. All females receive the dominant, red-eyed allele from their fathers and the recessive, white-eyed allele from their mothers.
(If necessary see the tutorial for problem #1 of the monohybrid cross problem set for a review of how to set up a Punnett Square.)
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Updated: July 15, 1999
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