Question

A population of green beetles (GG; Gg) lives in a specific habitat. The allele for color is represented by the colors on their backs. Over time, through random chance, the gene pool of the beetle population changes and more brown (gg) beetles are present in the population. How would you describe the sequence of events that lead to a change in allelic frequency?

Answer 1

Perhaps the habitat has changed, for example, dried up, so not much green vegetation.  The green beetles are thus more vulnerable, favouring the brown ones.  With less green beetles to take part in mating, relatively more g alleles are present, to the point that they become the majority.

Answer 2

Beetles with the brown allele immigrated into the population; the beetles mated and reproduced, incorporating the recessive allele into the gene pool.

We know nothing about the habitat; we only know about the alleles. It would make the most sense to infer that gene flow through immigration occurred to change the allelic frequency.