Question

Widow's peak, a pointed hairline on the forehead, is a genetic trait caused by a dominant allele. it can be traced back through a family's history using pedigree analysis. the pedigree shown here is of three generations of a family. notice that some individuals (shown in gray) have a widow's peak (w = dominant allele and w = recessive allele). this pedigree supports the fact that widow's peak is due to a dominant allele, because if it were due to a recessive allele and both parents show the recessive phenotype, then ________.

Answer 1

As you can see from the pedigree presented below, Joseph and Alice both have Widow's peak, but one of their children possesses the trait and the other doesn't. If this were a trait that was determined by a recessive allele, this would be impossible, because the two parents would possess two recessive alleles and their offspring could only get the recessive allele from them.
But because this is a trait determined by a dominant allele, an individual can have the trait, but also have offspring that do not possess the trait.