Blood group is controlled by alleles and (codominant) and (recessive). A mother of genotype and a father of genotype have a child. What is the probability the child has blood group O?

Answer and explanation

Correct answer: D.

  1. Step 1: The mother's gametes are or ; the father's gametes are or .
  2. Step 2: The four equally likely children are , , and .
  3. Step 3: Only is group O, so the probability is .
Answer
.
Why not the others: : is the probability that the child is group A or group B. : is the probability that the child is not group O. : treats the cross as a dihybrid cross.

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