The allele for a widow’s peak has complete dominance over the allele for a straight hairline (w). what is the probability of two parents heterozygous for a widow’s peak (ww) having an offspring with a widow’s peak?

The probability of having an offspring with widow's peak is 3/4.

Explanation-

Widow's peak is a dominant trait over straight hairline, which is a recessive trait. The allele for Widow's peak is W and for straight hairline is w.

The possible genotypes for the widow's peak are WW and Ww. The genotype for the straight hairline is ww.

As the parents are heterozygous, the genotype of the parents are Ww and Ww.

Using the punnett square, the probability of offspring with widow's peak = 3/4

This means that that there are 75% chances of having an offspring with the widow's peak.

3/4

Explanation:

The dominant allele is expressed as W and the recessive allele is expressed as w.

Since it is given that the parents are heterozygous their genotype would be Ww.

Now when you cross them you get,

Ww X Ww ---> WW Ww Ww ww

Now, W is dominant over w, therefore, the offsprings with the genotype WW and Ww will have a widow's peak whereas only the offspring with the genotype ww will have a straight hairline.

Therefore, from the result of the cross, we can see that 3 out of four offspring will have widows peaks, thus the probability is 3/4.

Please see the attached punnett square .