A mother with blood group O (phenotype) and genotype OO will have 2 children from a man with blood group A (phenotype) and genotype AO. The first child, a girl, has blood group O, and the second child, a boy, has blood group AB (the boy bears a striking resemblance to his father). What exceptions allow this? Mother has a third child (boy) with blood group B (phenotype B, genotype BO) in the same marriage. However, a DNA test (father-son y-test) between this legal father and son showed that they are not related. So he has a different causative agent. How can child 2 have a different blood group and yet be of the same causative agent as child 1? Could this be chimerism or a reactivating b allele?
Answer
Mendelian inheritance of blood groups makes this impossible in principle. The story of the third child makes it likely that the second child is also not the legitimate father’s. That should be checked first.
Answered by
dr. Mistiaen Wilhelm
Prinsstraat 13 2000 Antwerp
http://www.uantwerpen.be
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