Question

A certain white-fruited squash, self fertilized, produces some white and some yellow offspring. White is dominant. If there was 21 yellow, how many whites would be expected?* There is only one possible answer to this problem.

Answer 1

You're told that the white fruited squash self fertilized. That means that the genotype of the female gamete and male gametes came from the same plant. They are genetically identical.

You're told that the parent squash was white fruited, but that some of its offspring are yellow fruited. Because some of the offspring have a phenotype which differs from the phenotype of the parent, you know that those offspring have a recessive phenotype. That can only happen when they get a recessive allele from both parents.

So you know that the white fruited parents are heterozygous.

Is that much clear?

Answer 2

When you cross two heterozygotes (like in this case), what genotypic and phenotypic ratios do you exepect to see?

Answer 3

50-50

Answer 4

No.

You'd expect the genotypic ratio of the offspring to be 1/4 WW (homozygous dominant), 1/2 to be Ww (heterozygous) and 1/4 to ww (homozygous recessive).

What phenotypic ratios are associated with these genotypes?