Question

When a man has blood group (AB) marries a woman has blood group (O), the ratio of children which have blood group (O) is . . . . .
0%
50%
25%
75%

Answer 1

When a man with blood group AB (genotype IAIB) marries a woman with blood group O (genotype ii), the possible genotypes of their offspring are IAi, IBi, ii. The IAi and IBi genotypes would result in blood type AB, while the ii genotype would result in blood type O.
The Punnett square for this cross is:




I
A
i




i
IAi
AIi
ii



Therefore, the ratio of children with blood group O (ii genotype) would be 1 out of 4, which is 25%.