Question

The following phenotypic ratios are determined for a trihybrid cross in which the gametes assort independently: A 1 : A 2 =¼ : ¾ B 1 : B 2 =¼ : ¾ C 1 : C 2 = ¾ :¼ What is the probability that the F2 offspring will have the phenotype A 1 B 1 C 1?

1) 27/64
2) 9/64
3) 1/64
4) 3/64

Answer 1

The probability of the F2 offspring having the phenotype A1B1C1 in a trihybrid cross with independent assortment is calculated by multiplying the individual probabilities of each genotype: (1/4) × (1/4) × (3/4) = 3/64. The correct answer is option 4.

Step-by-step explanation:

The question deals with a trihybrid cross where the phenotypic ratios for the three independently assorting genes A, B, and C are given. We can use the product rule of probability to calculate the likelihood of obtaining the phenotype A1B1C1 in the F2 generation. Since the problem provides the ratio of dominant to recessive phenotypes for each gene, we multiply the probability for each genotype A1, B1, and C1.

For gene A, the A1 : A2 ratio is 1/4 : 3/4, which means the probability of A1 phenotype is 1/4. For gene B, the B1 : B2 ratio is also 1/4 : 3/4, so the probability of B1 phenotype is 1/4. Finally, for gene C, the C1 : C2 ratio is given as 3/4 : 1/4, with a probability of C1 phenotype being 3/4.

To find the probability of the F2 offspring having the phenotype A1B1C1, we multiply these probabilities together:

(1/4) × (1/4) × (3/4) = 3/64

Therefore, the correct answer is 3/64, which corresponds to option 4).