Question

For summer squash, the dominant allele for one gene leads to yellow color while the recessive allele for this gene leads to green color. When the genotype of a second gene is either homozygous dominant or heterozygous, neither color is produced and the squash is white. The effect of the second gene on the first one is called ______?

1) Incomplete dominance
2) Codominance
3) Epistasis
4) Polygenic inheritance

Answer 1

Epistasis is the interaction between genes where one gene masks or suppresses the expression of another. In summer squash, a dominant allele of the second gene causes the squash to be white, no matter the alleles of the first gene, which determine yellow or green squash.

Step-by-step explanation:

The effect of the second gene on the first one in the case of summer squash color is called epistasis. In this case, the presence of a dominant allele in the second gene masks the expression of the alleles in the first gene. If a homozygous dominant (WW or Ww) genotype is present, it will result in a white color squash, regardless of the yellow or green alleles (Y or y) from the first gene. If the genotype is homozygous recessive for the W gene (ww) together with a dominant Y gene (YY or Yy), it will produce yellow squash, while the homozygous recessive for both genes (wwyy) gives green squash. An example of this can be observed when crossing two white heterozygotes (WwYy x WwYy), resulting in a phenotypic ratio of 12 white squash, 3 yellow squash, and 1 green squash.