[Campbell Biology P.334] According to the Punnett square in Figure 14.16, if two carrier par... | Practice Question

According to the Punnett square in Figure 14.16, if two carrier parents Aa have a child with a normal phenotype, what is the probability that this child is also a carrier Aa ?

  • A: 1/4
  • B: 1/2
  • C: 2/3
  • D: 3/4

Explanation

From the cross Aa x Aa, the offspring genotypes are 1 AA : 2 Aa : 1 aa. The phenotypically normal offspring are the AA and Aa individuals, making a total of 3 possibilities. Among these 3, 2 are heterozygous Aa . Therefore, the probability of a normal-phenotype child being a carrier is 2/3. The text explicitly states this calculation.