What is the probability that they will have a child who has the same genotype as the father?

At two independently assorting loci, a man has the following genotype: GgHH. He marries a woman with the genotype ggHh.

What is the probability that they will have a child who has the same genotype as the father?
A . 0
B . 1/2
C . 1/4
D . 1/8

View Answer

Answer: C

Explanation:

This is a “probability” genetics question that can be answered by practical application of Mendel’s Laws. Mendel’s Law of Segregation states that alleles segregate during meiosis, resulting in gametes that carry only one allele for any given inherited trait (i.e., haploid gametes). Mendel’s Law of Independent Assortment states that unlinked genes assort independently during meiosis. By applying Mendel’s Laws, we can conclude that each parent in the problem can produce two possible gametes. The father can produce the gametes GH and gH, and the mother can produce the gametes gH and gh. The probability of the father’s genotype (GgHH) appearing in the progeny can be determined by calculating the number of different gamete combinations that will produce this genotype. Thus, a GgHH zygote can only be produced by the fusion of a GH gamete and a gH gamete. The probability that one parent will donate a particular gamete is independent of the probability that the other parent will donate a particular gamete. Thus, the probability of the father donating a GH gamete is 1/2, and the probability of the mother donating a gH gamete is 1/2. The probability of producing a genotype that requires the occurrence of both these independent events is equal to the product of the individual probabilities that these events will occur. Thus, 1/2 × 1/2 = 1/4, so the probability that this couple will have a child with the genotype GgHH is 1/4.