Question

need help justifying. i know it is C but not why

In a large, isolated population of an insect species, a specific gene locus has one dominant allele (A) and one recessive allele (a). The genotype frequencies of the gene were collected for ten generations, as shown in Table 1. Table 1. Genotypic frequencies over ten generations in an insect species ΑΑΙ Αα Generation 1 0.47 0.43 0.10 Generation 5 0.32 0.60 0.08 Generation 10 0.20 0.75 0.05 Which of the following could best account for the change in genotypic frequencies over the ten generations? (A) Because the A allele is unstable, over the course of the study most of the A alleles mutated to become a alleles (B) The population is in Hardy-Weinberg equilibrium, which allows for changes in genotypic frequencies every generation (C) The population is not exhibiting random mating between individuals. (D) The population is becoming extinct because the a allele is disappearing.

Answer 1

Over 10 generations, the homozygous organisms frequency is reduced while that of heterozygous individuals increased. It means that allele A is not mutated to a allele. So option (A) is wrong. Option (D) also says about disappearing of a alleles but as heterozygous individuals are increased, it is not possible.  

For options (B) and (C), the knowledge about hardy Weinberg rule is required. The rule states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.

But here in option (B), the genotype frequencies are changed from generation to generation, so the Hardy Weinberg rule is not followed. Hence the option is wrong. As for option C, absence of random mating is one of the factors to deviate from Hardy Weinberg rule, so option (C) is correct.