Question

having a widows peak hairline (shown below) is a dominant trait. if two parents who do not have a widows peak hairline (they have straight hairlines) have a child, what is the probability that the child will have a widows peak hairline?

Explanation:

Step1: Determine Genotypes of Parents

Since widow's peak (W) is dominant and straight hairline (w) is recessive, parents with straight hairlines must be homozygous recessive (ww). So both parents have genotype ww.

Step2: Analyze Gamete Production

Each parent can only produce gametes with the w allele (because their genotype is ww, so all gametes are w).

Step3: Determine Offspring Genotype

When we cross two ww parents, the possible offspring genotypes are determined by combining their gametes. The Punnett square for ww × ww will have all offspring with genotype ww (since w from parent 1 and w from parent 2 combine).

Step4: Determine Phenotype Probability

The genotype ww corresponds to the straight hairline phenotype (recessive trait). Since widow's peak is dominant (requires at least one W allele), and all offspring are ww, the probability of having a widow's peak (dominant trait) is 0.

Answer:

0 (or 0% probability)