Chapter 9, Problem 22PS

Interpreting Data As shown in the Punnett square below, albinism is caused by an autosomal recessive allele. Two parents who do not show any signs of albinism but are carriers could therefore have a child who displays albinism because that child could inherit one recessive albinism causing gene from each parent. Imagine that a male with albinism mates with a female who does not display albinism. We know the male with albinism must have the genotype aa, but the female could be either Aa or AA. Such a mating is essentially a testcross, like the one shown in Figure 910. If the parents' first child does not display albinism, can you say with certainty what the mother’s genotype must be? What if the couple has four children (none twins), none displaying albinism–can you say with certainty the mother's genotype? What would it take for a definitive genotype to be assigned?