Question

Yellow color in summer squash is determined by a single dominant allele, thus YY and Yy genotypes both produce yellow squash but yy does not. You cross summer squash to a zucchini, which is green and therefore yy. Among your 60 offspring, 100% are yellow. What are the frequencies of the Y and y alleles, respectively, among these 60 offspring?

a) 75%, 25%
b) 25%, 75%
c) 50%, 50%
d) 100%, 0%
e) Not enough information

Answer 1

When a yellow summer squash is crossed with a green zucchini, and all offspring are yellow, the frequency of Y alleles among the offspring is 50%, and the frequency of y alleles is also 50%, as each offspring inherits one allele from each parent. The correct answer is c) 50%, 50%.

Step-by-step explanation:

When you cross a yellow summer squash (YY or Yy) with a green zucchini (yy), resulting in 100% yellow offspring, you can infer that all the offspring have at least one Y allele.

Since all the offspring are yellow, we know they must all possess one dominant allele from the yellow summer squash parent, which can only be a Y, given that the zucchini parent can only contribute a recessive y allele.

As we have 60 offspring and each gets one allele from each parent, there are 60 Y alleles (from the summer squash) in the offspring. Since none of the offspring are green, we know that there are 0 yy combinations, and hence 0 y alleles contributed by the yellow squash parent.

Each offspring possesses one y allele from the zucchini parent, however, this is still outnumbered by the Y allele. Thus, the offspring's allele frequency is 60 Y alleles and 60 y alleles, making it 50% Y and 50% y.