Biology Practice Problems Extensions to Mendel Practice Problems Solution: Suppose two independently assorting genes are invo...

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Solution: Suppose two independently assorting genes are involved in the pathway that determies fruit color in squash. These genes interact with each other to produce the squash color seen in the grocery store.At the first locus, the W allele codes for a dominant white phenotype, whereas the w allele codes for a colored squash. At the second locus, the allele Y codes for a dominant yellow phenotype, and the allele y codes for a recessive green phenotype. The phenotypes from the first locus will always mask the phenotype produced by the second locus if the dominant allele (W) is present at the first locus. This masking pattern isk nown as the dominant epistasis.A dihybrid squash, WwYy, is selfed, and produces 128 offspring. How many offspring are expected to have each of phenotypes: white, yellow, orange?

Problem

Suppose two independently assorting genes are involved in the pathway that determies fruit color in squash. These genes interact with each other to produce the squash color seen in the grocery store.

At the first locus, the W allele codes for a dominant white phenotype, whereas the w allele codes for a colored squash. At the second locus, the allele Y codes for a dominant yellow phenotype, and the allele y codes for a recessive green phenotype. The phenotypes from the first locus will always mask the phenotype produced by the second locus if the dominant allele (W) is present at the first locus. This masking pattern isk nown as the dominant epistasis.

A dihybrid squash, WwYy, is selfed, and produces 128 offspring. How many offspring are expected to have each of phenotypes: white, yellow, orange?

Solution

Since the expression of the W/w gene precedes that of the Y/y gene, it can be estimated that a dihybrid cross will produce 3/4 white due to only a single dominant W allele is needed to produce them. Along with the second gene, Y/y, the Punnet square for this dihybrid cross is shown below:

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