9. in a small population of snails, one individual inherits a synonymous mutation in a gene that codes for an important protein. after 5 generations, 6 % of the snail population carries this mutation. what is the most likely explanation for this evolution?

Genetic drift

Explanation:

Genetic drift is one of the mechanisms that lead to evolution. Genetic drift refers to any chance event that brings about changes in the allele frequency of a population and leads to evolution of population with altered allele frequencies.  

Given that the population size of snail is small, genetic drift would be the most effective way to increase the frequency of the said mutation as small populations are more susceptible to get evolved by genetic drift. Therefore, genetic drift might have increased the frequency of the mutation in the population.