Question

In summer squash, white fruit is dominant over yellow color. If a heterozygous white squash is self fertilized, what will be the ratio of white to yellow squash in the offspring?

Answer 1

When a heterozygous white summer squash (Ww) is self-fertilized, the offspring exhibit a 12 white:3 yellow:1 green ratio instead of a simple 3:1, due to the epistatic effect of the dominant white gene over the yellow gene.

Step-by-step explanation:

When a heterozygous white summer squash (Ww) is self-fertilized, the offspring will demonstrate a phenotypic ratio of white to yellow squashes, governed by Mendelian genetics and epistasis. Given that white fruit color is dominant over yellow and the presence of even one dominant allele for the white gene (W) masks the expression of the yellow gene (Y), the expected phenotypic ratio in the offspring does not adhere to a simple 3:1 Mendelian ratio for a monohybrid cross. Instead, we must consider a dihybrid cross since two genes are involved.

Therefore, crossing heterozygous white squashes (WwYy x WwYy) will produce offspring with a 12 white:3 yellow:1 green phenotypic ratio. This is due to the epistatic effect of the W gene over the Y gene: white squashes will prevail whenever the W allele is present. The three yellow offspring arise from the homozygous recessive ww combination coupled with either YY or Yy alleles, while green offspring result from homozygous recessive forms of both genes (wwyy).