Question

genetic inheritance: predicting parent genotype from child phenotype
a couple has two children; one with a widows peak and one without. if both parents have a widows peak what do you know to be true?
multiple choice
both parents are homozygous dominant for the trait.
both parents are homozygous recessive for the trait.
both parents are heterozygous for the trait.
one parent is homozygous dominant, and one parent is heterozygous for the trait.
one parent is homozygous dominant, and one parent is homozygous recessive for the trait.

Explanation:

Let's assume the allele for widow's peak is \(W\) (dominant) and for no widow's peak is \(w\) (recessive).

• If both parents were homozygous dominant (\(WW\times WW\)), all offspring would have widow's peak (\(WW\)).
• If both parents were homozygous recessive (\(ww\times ww\)), all offspring would have no widow's peak (\(ww\)).
• If one parent is homozygous dominant (\(WW\)) and one is heterozygous (\(Ww\)), all offspring would have widow's peak (\(WW\) or \(Ww\)).
• If one parent is homozygous dominant (\(WW\)) and one is homozygous recessive (\(ww\)), all offspring would be heterozygous (\(Ww\)) and have widow's peak.
• If both parents are heterozygous (\(Ww\times Ww\)), using Punnett square:

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The phenotypic ratio is \(3\) (widow's peak) : \(1\) (no widow's peak). So it is possible to have children with and without widow's peak.

Answer:

Both parents are heterozygous for the trait.