Question

John and his grandmother are both homozygous for alkaptonuria, an autosomal recessive disease. John's grandmother has two brothers and a sister. One of the brothers had alkaptonuria and his daughter is John's mother. If John's parents decide to have another child, what is the probability of the child to be affected with alkaptonuria? Select the right answer and show your work on your scratch paper for full credit. od John O 0.5 o 5 1 0.75 0.25

please show all work

Answer 1

John's parents do not have the disease condition, wheras john does, so it means that both his parents have heterozygous genotypes. Since alkaptonuria is an autosomal recessive disorder John has received recessive alleles from both his parents. Let us consider the dominant and recesive alleles to be K and k. The genotype of john's parents is Kk and that of John's is kk. Let us draw the punnett square to determine the probability of the occurrence of the disease:

	K	k
K	KK Normal	Kk Normal
k	Kk Normal	kk Alkaptonuria

So, the probabilty of occurrence of the condition is 1/4 or 0.25

The probability of their second child contracting the disease is independent of whether or not the first child was affected. So the right answer here would be the last option, 0.25