Question

Dr. Paul is blood type O. His father was blood type A and his mother was blood type B. What were the genotypes of his parents and what are the possible blood types and ratios expected for crosses involving these parental genotypes?

Answer 1

Dr. Paul must have received an O gene from each parent, but they also had A (dad) and B (mom) genes. That should give you their genotypes. Using a Punnett square should answer your last question. (See one of SraJMcGin's sources.)

Answer 2

a