O-LevelBiologyGenetics & Variation5090/12 · May/June 2023 · Q351 Mark

Two brothers had different blood groups. One was blood group A and the other was blood group B. What can be concluded about their parents' blood group genotypes?

ABoth of the parents must be heterozygous.

BBoth of the parents must be homozygous.

COne parent (at least) must be heterozygous.

DOne parent (at least) must be homozygous.

✓ Correct answer

C: One parent (at least) must be heterozygous.

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Topic: Genetics & Variation, O-Level Biology (syllabus 5090). Multiple choice, 1 mark.
Source: O-Level Biology, May/June 2023 Paper 1 Variant 2, question 35.

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