[Campbell Biology P.326] To calculate the probability of an F2 offspring being heterozygous ... | Practice Question

To calculate the probability of an F2 offspring being heterozygous Rr , which rule of probability should be used and why?

  • A: The multiplication rule, because the egg and sperm must both carry the same allele.
  • B: The addition rule, because there is only one way to form a heterozygous offspring.
  • C: The addition rule, because a heterozygous offspring can be formed in two mutually exclusive ways.
  • D: The multiplication rule, because the events are not independent.

Explanation

A heterozygous offspring Rr can be formed in two ways: the egg is R prob 1/2 AND the sperm is r prob 1/2 , OR the egg is r prob 1/2 AND the sperm is R prob 1/2 . The probability of the first way is 1/4 multiplication rule . The probability of the second way is also 1/4. Since these are mutually exclusive events, we use the addition rule to find the total probability: 1/4 + 1/4 = 1/2.