Jack is O - blood type and his wife Jill is AB + blood type. Jill's father has B - blood type. What percentage of their children are expected to have A - blood type?

There is 25% chances for delivering a baby with A-ve.

Explanation:

AB + is a dominant blood group and O is a recessive blood group. To understand that Jill has AB + blood type with her father having B - blood type she should have acquired her AB + from her mother who had A + blood type.

When mother has this dominant AB + blood type and father with the O - Recessive blood type there are likely chances only for the dominant alleles to take charge over the recessive ones. Hence there is a chance of the babies to have both A-, A + blood group and B + ve or B - ve blood group.

As the mother has her Rh - ve inscribed in her DNA from her father she is a carrier and when joined with Rh - ve from her husband there are 25% chances for delivering a baby with A-ve.