36.People with nailpatella syndrome have poorly developed or absent kneecaps and nails. Individuals with alkaptonuria have arthritis as well as urine that darkens when exposed to air. Both nailpatella syndrome and alkaptonuria are rare phenotypes. In the following pedigree, vertical red lines indicate individuals with nailpatella syndrome, while horizontal green lines denote individuals with alkaptonuria.
a. What are the most likely modes of inheritance of nailpatella syndrome and alkaptonuria? What genotypes can you ascribe to each of the individuals in the pedigree for both of these phenotypes?
b. In a mating between IV2 and IV5, what is the chance that the child produced would have both nailpatella syndrome and alkaptonuria? Nailpatella syndrome alone? Alkaptonuria alone? Neither defect?
First, I got a). IV2 has genotype of nnA_ and IV5 has Nnaa.
For b), the textbook manual says the chance of their child having both nail-patella and alkaptonuria is: (1/2) chance of IV2 receiving Aa x (1/2) chance of IV2 donating n a gamete x (1/2) chance of IV5 donating n a gamete
= 1/8.
But isn't the chance of IV2 having Aa alleles dependent on his father, III2? Since III2 also has genotype nnA_ and III1 has nnAA, his son can only be a carrier of Alkaptonuria when his father is a carrier. So should I have to multiply by another 1/2, chance of his father being a carrier then multiply the rest (1/8)= 1/16?
I know how to do the rest of question. Any help would be appreciated.