Marion has a baby boy named Ralph. She also claims that Mr. Smith is Ralph's father. Marion is blood type B; Ralph is blood type B, and Mr. Smith is bloodtype A. Is it possible that Mr. Smith is the dad? If so what are Ralph's and Mr Smith's genotype?
To deal with the possibility that Ralph is a son of Mr Smith, we have to deal with their genotypes and do some punnett squares of it.
Marion has a blood type B (genotype BB or BO)
Raplh has a blood type of B (genotype BB or BO)
Mr. Smith has a blood type of A (genotype AA or AO)
Now since we do not know what genotype each parent has, we have to make possible combinations.
Father x Mother
AA x BB
AO x BB
AA x BO
AO x BO
1. AA x BB will produce 100% AB offspring
2. AO x BB will produce 50% AB and 50% BO offspring
3. AA x BO will produce 50% AB and 50% AO offspring
4. AO x BO will produce 25% AB, 25%AO, 25% BO and 25% OO offspring.
We know that Ralph has a blood type of B that can have a genotype of BB or BO. Since genotype BO shows in the matching of the parent’s genotypes (2 and 4), there is a possibility that Mr Smith is Ralph's father.
Mr Smith can be the father of Ralph if and only if Mr Smith's genotype is AO and Ralph's genotype is BO.