In humans, alkaptonuria is a metabolic disorder in which affected persons produce black urine. Alkaptonuria results from an allele (a) that is recessive to the allele for normal metabolism (A). Sally has normal metabolism, but her brother has alkaptonuria. Sally's father has alkaptonuria, and her mother has normal metabolism.
(a) Give the genotypes of Sally, her mother, her father, and her brother.
(b) If Sally's parents have another child, what is the probability that this child will have alkaptonuria?
(c) If Sally marries a man with alkaptonuria, what is the probability that their first child will have alkaptonuria?