Chapter 17, Problem 22P

The human IGF2 gene is autosomal and maternally imprinted. Copies of the gene received from the mother are not expressed, but copies received from the father are expressed. You have found two alleles of this gene that encode two different forms of the IGF2 protein distinguishable by gel electrophoresis. One allele encodes a 60K (Kilodalton) blood protein; the other allele encodes a 50K blood protein. In an analysis of blood proteins from a couple named Bill and Joan, you find only the 60K protein in Joan’s blood and only the 50K protein in Bill’s blood. You then look at their children: Jill is producing only the 50K protein, while Bill Jr. is producing only the 60K protein.

a.	With these data alone, what can you say about the IGF2 genotype of Bill Sr. and Joan?
b.	Bill Jr. and a woman named Sara have two children, Pat and Tim. Pat produces only the 60K protein and Tim produces only the 50K protein. With the accumulated data, what can you now say about the genotypes of Joan and Bill Sr.?