g In humans, a widow's peak hairline is dominant while a straight hairline is recessive. Tom and Sue both have a widow's peak but their son Joe has a straight hairline. If they have another child, what is the genetic probability of that child having a widow's peak hairline

3/4

Explanation:

In humans, a widow's peak hairline is dominant while a straight hairline is recessive.

Tom and Sue both have a widow's peak but their son Joe has a straight hairline.

For Joe to have a straight haircut which is inherited in the recessive condition, that means both parent each has a recessive allele copy for this trailer making them heterozygotes for the trait.

If the widow's peak allele is W (genotype for heterozygote would be Ww)

A cross between these two heterozygotes gives

Ww x Ww

WW Ww Ww ww

3/4 widow's peak 1/4 straight hair line

The genetic probability of that child having a widow's peak hairline is 3/4 ...