Question

Sarah has type A blood, and Jesse has type O blood. Their son has type B blood. Can Jesse be the baby daddy? He is a bit worried.

Please complete the Punnett squares to determine the possibilities.

a
Yes, if both parents are heterozygous
b
No, this is impossible
c
Yes, if one parent is heterozygous
d
No, type B blood must be homozygous

Answer 1

c. Yes, if one parent is heterozygous

Since Sarah has type A blood (genotype could be AA or AO) and Jesse has type O blood (genotype is OO), their son having type B blood (genotype must be BO) is possible if Sarah is heterozygous (genotype AO).

Punnett square:
| A | O |
-----------------
B | AB | BO |
O | AO | OO |