Question

4c) A woman with blood group 'A' (heterozygous) claimed that her son who has blood group 'O' was fathered by Mr. James who has blood group 'A' (homozygous). With the aid of suitable genetic diagrams (i) prove or disprove the woman's claim (ii) give reasons to support your answer. [10 marks]

Accepted Answer

Homozygous 'A' (Mr. James) = AA. Heterozygous 'A' (mother) = AO.
If Mr. James is AA (homozygous), he can only pass on the A allele to any child. Since blood group O requires the genotype OO (an O allele from each parent), and Mr. James has no O allele to give, he cannot be the father of a blood-group-O child.
(i) The woman's claim is disproved.
(ii) Mr. James, being homozygous AA, cannot pass on an O allele; a blood-group-O child (OO) requires an O allele from both biological parents, which is impossible in a cross with a homozygous-AA father.

WAEC Biology 2010 Theory — Question 13

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