Sex-Linked Inheritance Problem Set 2

Problem 4: Genetic evidence for crossing over in male flies

Tutorial to help answer the question

If we mated the F1 female and male flies from the cross obtained in problem 3, what male phenotype in the F2 generation would be evidence that crossing over had occured during gamete formation?

Daughters were tan-bodied, red-eyed, heterozygous for both eye and body color. The sons were yellow-bodied, red-eyed hemizygous.


Genotypes and phenotypes of parents

The F1 female's eggs will have either a red-eyed, yellow-bodied X chromosome or a white-eyed, tan-bodied one.

The F1 male's sperm will have either the red-eyed, yellow-bodied X chromosome or the Y chromosome.

Genotype and phenotype of non-recombinant male offspring

Without recombination, the male offspring would have the parental X chromosomes with the combinations of alleles of yellow body/red eyes and tan body/white eyes.

Genotype and phenotype of recombinant male offspring

Evidence for recombination between X chromosomes in the F1 female would be a new combination of alleles not present on any of the X chromosomes of the parents of the F1 female.

Yellow body/white eyes and tan body/red eyes F2 males would be evidence of crossing over.

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Updated: July 15, 1999
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