The phenotype of type A blood can be produced by the following genotypes-- homozygous AA or heterozygous AO. Since the gene for A is dominant to O, the combination of AO will still result in a person with type A blood. Since we only know the parents blood type is A, if each parent is AA, then the offspring will be type A also. However, if each is type A with the genotype of AO, there is a 1 in 4 chance of producing a child with type O blood. The phenotype of O is produced when two O genes are inherited by the child.
Because the father has Rh negative blood, the only genotype that will produce that phenotype is two Rh negative genes. This is a recessive trait.
The mother has Rh positive blood. This can be produced by either two Rh positive genes, or one Rh positive and one Rh negative gene. Therefore, in this couple, if the father is (--) and the mother is (++), the child will be heterozygous but Rh positive(+-). Or, another possibility is that if the mother is heterozygous (+-) and the father is (--), the offspring will have a 50% chance of being Rh positive (+ ) and a 50% chance of being Rh negative ( -).
If we take into account the blood type and the Rh factor, the offspring of this couple can be type A or O and Rh positive or negative.