Biology Practice Problems Genetic Counseling Practice Problems Solution: The mutant strain maroon-like has an X-linked muta...

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Solution: The mutant strain maroon-like has an X-linked mutant allele (Xm) that results in deep maroon-colored eyes in homozygous females and hemizygous males. To prove to a skeptical friend that this trait is in fact X-linked, you set up a reciprocal cross against the wild type. What are the expected genotypic and phenotypic frequencies of each half of this crossing experiment?

Problem


The mutant strain maroon-like has an X-linked mutant allele (Xm) that results in deep maroon-colored eyes in homozygous females and hemizygous males. To prove to a skeptical friend that this trait is in fact X-linked, you set up a reciprocal cross against the wild type. What are the expected genotypic and phenotypic frequencies of each half of this crossing experiment?

Solution

For the cross between a mutant male and a female that is wild-type for the trait, the Punnet square for their offspring is shown below:

Here, it can be seen that the genotype ratio is 1 XmX+ : 1 X+Y. The phenotype for all offspring would be that of a wild type. This shows that the trait is recessive as it skipped a generation. 

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