A man with homozygous A (AA) can only give alleles for Type A blood. A person with type O blood will always be homozygous for O (OO) since Type O is recessive, so the woman has to be homozygous for O. The children will all receive an A allele from the father, and an O allele from the mother, meaning that 100% of their children will be heterozygous for Type A blood (AO).
