Question

A father with type B blood and mother with type A blood have a child. Their child, while in a biology lab at school, tests her blood and discovers she has type O blood. Does she have any concerns about her parentage?

A. Yes, because she should have type AB blood if they are her true biological parents.
B. No, because type O blood is possible if her parents both had genotypes AB.
C. No, because both of her parents could be heterozygous.
D. Yes, because both of her parents might be heterozygous.
E. No, because blood types A and B are codominant.

Answer 1

C. if the father was B, the mother was A, and the child had O, then the father had to be Bi and the mother had to be Ai

Answer 2

C. you can have an A or B blood type but also have recessive genes that could give an O if parent were heterozygous, like if the mother was A-i (i being recessive gene that could give 'O') and the father was B-i then if you do a punnett square then you can see that there's a 25% chance she has i-i or type O blood.