One of the traits that we looked at in class was a widow's peak (has peak is dominant, no peak is recessive). For each individual described below, indicate what we can determine about their genotype from their phenotype. Individual is bald, so can't tell whether or not they have a widow's peak, but neither parent has a widow's peak Answer 1 Individual has a widow's peak Answer 2 Individual can't roll their tongue Answer 3 Individual has a widow's peak, but their mother does not have a widow's peak Answer 4 If an individual does not have a widow's peak, which genotype (or genotypes) would be impossible for their children

Explanation: 1) Individual who is bald but neither parents has a widow's peak: As having a peak is dominant and the individual is bald with parents that doesn't have the trait, the genotype is recessive, in the case ww;

2) Individual has a widow's peak: The individual's genotype can be WW, homozygous for the trait or Ww, heterozygous for the trait, depending on the genotype of the parents;

3) Individual can't roll their tongue: Being able to roll the tongue is a dominant characteristics, so if the individual can't roll their tongue means the genotype is recessive. But, there is little evidence that this trait is dominant or inheritable;

4) Individual has a widow's peak but their mother does not: In this case, the genotype of the individual is heterozygous (Ww), because the mother is recessive (ww) and the offspring has the trait, so the father must have had it;

5) If an individual does not have a widow's peak (ww), which genotype would be impossible? If this individual crosses over with another individual with the same trait, their children will be all recessive for widow's peak (ww), so there is no possibility of an offspring with the trait;

If the initial individual crosses over with an individual with widow's peak, two possiblities can occur:

If the crossover is with an individual homozygous for the trait (WW): all their children will have widow's peak with genotype Ww. So, the possibility of not having the peak is 0;
If the crossover is with an individual heterozygous for the trait (Ww), there will be a probability of 25% for the children to have genotype WW, a probability of 50% for the offspring to be heterozygous (Ww) and has the trait and probability of 25% to be recessive (ww) and therefore doesn't have the trait;