The woman has the fourth blood group; the husband is the first and their son is also the fourth. Which of the parents has a step-child?
If the husband has the first blood group, then his genotype is I (0) I (0). This means that all of his children must have the I (0) gene. The mother has a fourth blood group, which means that her children must have genes either genotypes I (A) or I (B). The child has the fourth blood group, which means his genotype is I (A) I (B). Consequently, this child cannot be related to the father.
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