Final answer:
In the one-island model, you can ignore the proportion of island emigrants, since the model assumes insignificant gene flow from the island to the much larger mainland population. Genetic drift, which is the effect of chance on allele frequencies, occurs more rapidly in smaller populations, like those typically found on islands.
Step-by-step explanation:
In the one-island model, the quantity you can ignore is the proportion of island emigrants. This model focuses on the genetic variation within a small, isolated population and the genetic influence of a larger, nearby mainland population. The assumption is that there's a constant influx of genes from the mainland to the island, but the reverse (gene flow from the island to the mainland) is negligible because the mainland population is so large that the immigrants from the island have an insignificant effect on the overall allele frequencies of the mainland.
Genetic drift is a mechanism of evolution that refers to changes in the allele frequencies of a population due to random sampling. This process would indeed happen more quickly on an island compared to the mainland, primarily because island populations are typically smaller in size. Smaller populations experience more pronounced effects of genetic drift, as chance events can significantly alter allele frequencies if they affect a large proportion of the breeding individuals in the population.