A man has a pointed frontal hairline known as a widow's peak. This trait is thought to be controlled by a dominant allele. His wife lacks a widow's peak, and their son has a widow's peak. (W: widow's peak; w: no widow's peak). The son is curious about whether his father is homozygous or heterozygous for the widow's peak trait. Which of the following facts would allow him to know?a. His father's mother lacks a widow's peak.
b. Both his paternal grandfather and his paternal grandmother have widow's peaks.
c. The son's sister has a widow's peak.
d. The son's own daughter lacks a widow's peak.
e. The son submits his own blood sample to a local genotyping lab, and it establishes that he is heterozygous for the trait.

To find out if you are homozygous or heterozygous, you need to find out the genotype of your parents. This you do by looking at their phenotype, their grandparents, uncles. After that it's easy to find out if it's homo or heterozygous. Of course, this need not even be done when it is a characteristic determined by recessive alleles, but in the case of a characteristic determined by dominant alleles, such as widow's peak (W), we must visualize the characteristic in the individual's country.

Since the man, shown in the question above, has widow's peak, so that your child knows if he is homozygous or heterozygous, just look at whether the trait is present in this man's parents. If his mother doesn't have widow's peak, we automatically know that the man is heterozygous, and that was his father's estate. However, if this man's mother has widow's peak and his father does, then the man is homozygous.