There are three alleles controlling the ABO blood types.IA and IB are codominant genes so that the combination IAIB produces the AB blood type.The third allele,i,is recessive to the other two alleles.Which of the following combinations of parents (with blood types on the left)and child (with blood type listed on the right)is NOT possible?
A) A ´ AB = B
B) A ´ O = A
C) A ´ B = O
D) A ´ AB = O.
E) A ´ AB = B.

Question

There are three alleles controlling the ABO blood types.IA and IB are codominant genes so that the combination IAIB produces the AB blood type.The third allele,i,is recessive to the other two alleles.Which of the following combinations of parents (with blood types on the left)and child (with blood type listed on the right)is NOT possible?  
A) A ´ AB = B
B) A ´ O    = A
C) A ´ B    = O
D) A ´ AB = O.
E) A ´ AB = B.

Quizplus · Accepted Answer

A parent with type A only has IAIA or IAi alleles, and a parent with type AB has IAIB alleles. Therefore, it is impossible for their child to have type O, which requires ii alleles. A cross between A and AB (IAi x IAIB) can only produce A, B, or AB blood types.

There Are Three Alleles Controlling the ABO Blood Types