Question

A population of birds lives on a small island. Another population of the same species lives on the mainland. The distance between the island and the mainland is too great for birds to fly back and forth. Recently, a series of sandbars and tiny islands have formed between the island and the mainland.

What is the most likely effect of this?
an increase in mutations in both bird populations
an increase in gene flow between the bird populations
an increase in genetic drift between the bird populations
an increase in mutations in the island population

Answer 1

an increase in gene flow between the bird populations

Explanation: the sandbars/tiny islands create "stepping stones" that allow individuals to move and breed between island and mainland, increasing migration and gene flow. This would tend to homogenize allele frequencies and reduce the effects of genetic drift; it does not directly change mutation rates.