Two heterozygous parents (Aa x Aa) have a child. What is the probability that the child is aa, if A is dominant over a?
Answer and explanation
Correct answer: D. One in four (25 percent)
- Step 1: Each parent gives A or a with equal chance. Step 2. The four combinations AA, Aa, aA, aa are equally likely, so aa has probability 1/4. Answer: 1/4. Why not the others: 3/4 is the chance of the dominant phenotype, and carriers can still have aa children.
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