Inheritance of Blood types : Genotypes

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The probability that the child will be type A is 0.50. When you say that the woman's genotype is Rh+, that really is not a genotype, but a phenotype. She could be Rh+Rh+ or Rh+Rh-. IF you assume that she is homozygous Rh+Rh+, then the chance of having an Rh- child is 0. If, on the other hand, you assume that she is heterozygous, then the probability of having an Rh- child is 0.5. Combining those two probabilities, (and with making the assumption that she is heterozygous Rh+Rh-), the chance of having a type A Rh- child would be 0.5 X 0.5 = 0.25.