Solutions For An Introduction to Genetic Analysis Chapter 2 Problem 70P

Consider the mother (III2) of the child. Her sister III3 is having the disease, she is homozygous recessive. So, both her parents, II2 and II3 should be heterozygous, for this recessive allele to produce an affected child III3.

As both parents are heterozygous, the mother of the child that is III2 would be heterozygous, for this allele. As her sister got that disease, the probability of the mother of the child to be heterozygous is.

If we consider the father of the child, one of parents of the father should be carriers, as his grandfather is having the disease and was homozygous, for the recessive allele. So, the probability father being a carrier is.

Both the heterozygous parents giving the recessive allele to the child are 1/4. The risk of the child having the disease is: