Final answer:
In a trihybrid cross, the probability of obtaining a triply recessive F2 phenotype is calculated by multiplying the probability of each gene being homozygous recessive. This results in a probability of (1/4) × (1/4) × (1/4), which equals 1/64.
Step-by-step explanation:
The question asks about the probability of obtaining an F2 phenotype that is triply recessive in the case of a trihybrid cross between two true-breeding homozygous individuals with contrasting phenotypes. In a trihybrid cross, each trait can be considered independently due to Mendel's Law of Independent Assortment. Using a probability method, the chance of an offspring being homozygous recessive for each gene is 1/4, and for three genes, it is (1/4) × (1/4) × (1/4).
Therefore, to determine the probability of F2 offspring being triply recessive for all three traits, we multiply the individual probabilities together: (1/4) × (1/4) × (1/4), which equals 1/64. This means that the probability of an F2 phenotype being triply recessive in a trihybrid cross is 1/64.