In a particular human family, john and his mother both have brachydactyly (a rare autosomal dominant causing short fingers). john's father has huntington disease (another rare autosomal dominant). john's wife is phenotypically normal and is pregnant. two-thirds of people who inherit the huntington (hd) allele show symptoms by age 50, and john is 50 and has no symptoms. brachydactyly is 90% penetrant. a. what are the genotypes of john's parents? b. what are the possible genotypes for john? c. what is the probability the child will express both brachydactyly and huntington disease by age 50 if the two genes are unlinked? d. if these two loci are 20 m. u. apart, how will it change your answer to part c?