Question

The alleles for human blood types A and B are co-dominant but both are dominant over the type O allele. The Rh factor is separate from the ABO blood group and is located on a separate chromosome. The Rh-positive allele is dominant over Rh-negative. Indicate the possible phenotypes from the mating of a woman with type O Rh-negative with man with type A Rh-positive?

Help I don't get this at all?
Would the offspring have a 50/50 % chance of being either type A or type O?

Answer 1

This is quite an involved problem.

You are given the phenotypes of the parent. To tell what sort of offspring they might have you need to think about what their genotypes are and what alleles they might pass on to their offspring.

Consider the two genes for ABO blood type and Rh group separately.

You know that the Mom is O. Because both A and B are dominant to O, and because she has the wholly recessive phenotype, she must be OO. The man is A. That phenotype is consistent with two possible genotypes: he could be AA or AO.

You know that Mom is Rh negative. Again, she shows the wholly recessive phenotype so she must be (-)(-), where I use the negative sign to indicate Rh negative. The man is Rh positive. Again, he could be either homozygous dominant (+)(+) or a heterozygote (+)(-).

The possible outcomes depend on whether the man is homozygous dominant or heterozygous for both or either trait. If he is AO, then half the children will be AO and half will be OO, but if he is AA then all the children will be AO. Similarly with the other gene, if the man is (+)(+), then all the children will be (+)(-), but if the man is (+)(-), then half the children will be (+)(-) and the other half will be (-)(-).

Hope that's helpful.