Question

Figure 11.7 Do you think genetic drift would happen more quickly on an island or on the mainland?

Short answer

Genetic drift would likely happen more quickly on an island because island populations are often smaller and more isolated, which allows for faster changes in genetic makeup.

Step-by-step solution

Defining Genetic Drift

Genetic drift is a mechanism of evolution that causes random fluctuations in allele frequencies in a population. It happens due to random events, rather than natural selection, and can lead to significant changes in the genetic makeup of a population, especially if the population is small.

Consider the Effect of Population Size

Generally, genetic drift occurs more rapidly in smaller populations. This is because in small populations, chance events can result in large swings in allele frequencies from one generation to the next.

Consider the Isolation of Population

Populations in isolated locations, like islands, are often small and receive few new immigrants. Therefore, genetic drift can have a larger impact because there is less opportunity for new genetic variations to enter the population.

Contrast with Mainland Population

On the mainland, populations are generally larger and receive more immigrants, adding new genetic variation frequently. Therefore, the impact of genetic drift is typically less on the mainland because large populations buffer against the effects of random genetic drift, and new genetic material is constantly introduced.

Conclude and Answer the Question

Therefore, genetic drift would likely occur more quickly on an island than on a mainland, mainly due to the smaller population size and relative isolation of the island population.

Key concepts

Allele Frequencies

The genetic variation in a population is largely defined by allele frequencies, which represent the proportion of different versions of a gene, or alleles, amongst the individuals. Imagine a garden of flowers. If most of the flowers are red, the allele for red color is high in frequency. But one season, a rare storm wipes out many red flowers, leaving behind a few yellow ones. Suddenly, the garden's color composition changes. This mirrors what can happen in populations when rare, random events shift the allele frequencies, a process central to genetic drift.

Mechanism of Evolution

Evolution is often mistakenly thought to occur solely through natural selection, where traits that confer survival and reproductive advantages become more common. However, Genetic drift is another key evolutionary mechanism, wherein random, chance events, rather than advantageous traits, influence which genes become more or less common. For instance, if a boulder randomly rolls down a hill and crushes some beetles, the genes of the surviving beetles will be more common by chance, not by fitness, guiding the evolutionary path of the beetle population.

Population Size

Size does matter when it comes to genetic drift. In small communities, such as a secluded village, the birth or death of even one individual can significantly impact the genetic composition. This is similar to a scenario where flipping a coin three times can easily result in all heads or tails by chance, reflecting a significant shift. Conversely, flipping a coin hundreds of times leads to a more predictable distribution of heads and tails, highlighting how larger groups can dampen the influence of chance, thus making genetic drift less pronounced.

Isolation of Population

Isolation acts like a genetic gatekeeper, controlling the flow of new alleles into a population. On an island, the population is somewhat like a closed party with a strict guest list—newcomers are rare, and the gene pool is mostly limited to the existing inhabitants. This isolation amplifies the effects of genetic drift as the already small allele variation can drastically change with a single random event. Compared to a bustling city where newcomers are frequent, offering a constant influx of new genes, the changes in gene frequencies on an island can be much more drastic and swift.