Final answer:
Genetic drift has a dramatic effect on allele frequencies particularly in small populations because the genetic contribution of each individual is more significant. A single organism's genes can represent a considerable fraction of the overall gene pool, meaning that genetic drift can lead to substantial shifts in allele frequencies.
Step-by-step explanation:
Genetic drift can cause dramatic shifts in allele frequencies when the population is small. Genetic drift is a process where allele frequencies change due to random events rather than natural selection. In small populations, each individual carries a larger portion of the gene pool, so the loss or addition of alleles from the population can significantly affect overall genetic diversity.
The correct answer to the question is 1) small. The likelihood of genetic drift increases as the population size decreases. For instance, the demise of a single organism in a small population can result in a substantial genetic impact. This is because a small number of individuals are responsible for passing on genes to the next generation, so any changes, like a death or failure to reproduce, can lead to big changes in the population's genetic makeup. On the other hand, in larger populations, the genetic contribution of a single individual is diluted among many, making genetic drift less impactful.