Question

Inheritance of fruit color in summer squash provides an example of the phenomenon of epistasis. Yellow fruit is produced by a cross involving the homozygous recessive expression of the W gene (ww]) and either the homozygous dominant (YY) or heterozygous (Yy) form of the Y) gene. The wwyy outcome is green fruit. White fruit arises whenever a dominant copy of the W gene is involved in the cross, regardless of the Y alleles present. A cross of white WwYy heterozygotes produces the phenotypic ratio of 12 white : 3 yellow : 1 green fruits.

What is the best explanation for the phenotypic ratio of 12 white : 3 yellow : 1 green fruits in a cross of white WwYy heterozygotes in summer squash?
a) Independent assortment of genes
b) Codominance
c) Epistasis
d) Incomplete dominance

Answer 1

Epistasis is the correct explanation for the 12:3:1 phenotypic ratio of white, yellow, and green fruits in a cross of WwYy summer squash, as a dominant W allele masks the expression of the Y gene.

Step-by-step explanation:

The best explanation for the phenotypic ratio of 12 white : 3 yellow : 1 green fruits in a cross of white WwYy heterozygotes in summer squash is epistasis. This phenomenon occurs when the expression of one gene is masked by a dominant allele of another gene. In this case, the presence of a dominant W allele overrides the expression of the Y gene, resulting in white fruit.

When a cross of WwYy x WwYy is performed, we see that the W gene is epistatic to the Y gene, leading to a majority of white offspring. The yellow and green squash appear only when the W gene is homozygous recessive (ww), with the ratio of yellow (wwY_) to green (wwyy) offspring reflecting a typical monohybrid 3:1 ratio for the Y gene when its expression is not masked by the W gene.