Mary has type A blood and her husband (John) has type B blood. John's parents both had type AB. Mary and John have three children, one with type A, one with type AB, and one with type B. Relatives suspect that one of the children was adopted. What are Mary and John's blood genotypes, which child was adopted?

Question

Mary has type A blood and her husband (John) has type B blood.  John's parents both had type AB. Mary and John have three children, one with type A, one with type AB, and one with type B. Relatives suspect that one of the children was adopted.  What are Mary and John's blood genotypes, which child was adopted?

aaronq · Answer

>Mary has type A blood and her husband (John) has type B blood

Mary can be AO or AA

John can be BO or BB

>John's parents both had type AB.

John can only get A or B alleles, not O, so he must be BB

>have three children, one with type A, one with type AB, and one with type B. 

first  AO or AA
second AB 
third BB or BO

we know that John can only give the B allele, so all his children must have at least 1 B allele.

the first is AO or AA, and doesnt have a B allele.