A man is brought to court in a paternity case. He has blood type B, Rh positive. The mother has blood type B,?

Question

A man is brought to court in a paternity case. He has blood type B, Rh positive. The mother has blood type B, Rh negative. which blood type of a child would exclude the accused from paternity?

Answer 1

Either type A or type AB. As type B, he is either BB or BO, so the only possible alleles he can pass are on are the B and O alleles. Since the mom is also B, she could only pass on the same alleles. Possible test crosses would look like:

..... B B
B BB BB
B BB BB

..... B 0
B BB BO
B BB BO

..... B O
B BB BO
O BO OO

The baby could only be type B (BB or BO) or type O (OO), leaving type A and AB blood types to exclude him. Since he is Rh+ and she is Rh-, the baby could be either if he is +/- for his genotype.

.. + -
- +/- -/-
- +/- -/-

Answer 2

Only blood type A would exclude the accused. The Rh factor doesn't matter in this case. Since the mother doesn't carry a type A gene, the child could only get one from his/her father. The accused man is also type B (not AB) and hence doesn't have the necessary gene.

Type O would NOT exclude this man. Both parents show type B blood, but could each be carriers of the recessive O gene. That type would only appear in progeny, if each parent carried an O gene (and each contributed one).

Answer 3

A DNA paternity test can provide conclusive proof of whether the man is the father or not. They are painless and cost about $100.