A genetics counsellor in Port of Spain is advising a couple about their risk of having a child with a genetic disorder. The father is heterozygous (Aa) and the mother is homozygous recessive (aa) for the condition. What percentage of their children would be expected to be carriers?

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Question

A genetics counsellor in Port of Spain is advising a couple about their risk of having a child with a genetic disorder. The father is heterozygous (Aa) and the mother is homozygous recessive (aa) for the condition. What percentage of their children would be expected to be carriers?

Accepted Answer

50% — Award 1 mark for correct calculation. Cross Aa × aa produces Aa and aa in equal proportions (50% each). Only Aa individuals are carriers (heterozygous with one copy of the recessive allele). B is incorrect — carriers will be produced. C is incorrect — this is not the ratio from this cross. A is incorrect — only half the offspring will be carriers; the other half will be affected (aa).

Answer

50%

Answer

100%

Answer

25%

Answer

0%

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