Two unaffected parents have an affected child. What does this suggest about the condition?

Answer and explanation

Correct answer: D. It is recessive and both parents are carriers

  1. Step 1: A dominant condition always shows in carriers, so the parents cannot carry it silently.
  2. Step 2: The affected child must have inherited a recessive allele from each parent, so both are carriers.
Answer
It is recessive and both parents are carriers.
Why not the others: It is dominant and one parent is affected: an affected parent would have shown the condition. It is Y-linked and inherited from the father: the parents are unaffected and the child's sex is not specified. It is codominant and both parents show a mixed phenotype: unaffected parents show no sign of the condition.

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