Question

Galápagos medium ground finches are found on Santa Cruz and San Cristóbal islands, which are separated by about \(100 \mathrm{km}\) of ocean. Occasionally, individuals from either island fly to the other island to stay. This can alter the allele frequencies of the population through which of the following mechanisms? a. natural selection b. genetic drift c. gene flow d. mutation

Short answer

c. gene flow

Step-by-step solution

Recognize the different mechanisms of evolution

The four given terms are all mechanisms of evolution. Natural selection is a process where organisms better adapted to their environment tend to survive and produce more offspring. Genetic drift refers to changes in the gene pool of a small population due to chance. Gene flow is the transfer of genetic diversity or genes from one population to another and mutation is a random alteration of gene sequence that leads to a change in the sequence of DNA and therefore the function of the gene. In this case, the traveling of individuals from one island to the other introduces new genes to the other island's population, which fits the description of gene flow.

Match the situation with the mechanism

From the given information, there is nothing about the individuals' survival or reproduction rates being influenced by their traits (which would suggest natural selection), no emphasis on the smallness of the population leading to chance fluctuations (which would suggest genetic drift) or any mention of a change in genetic sequences resulting in a genetic variation (which would be mutation). However, these individuals from either island flying to the other can introduce new genes into the population they migrate to, which directly translates to gene flow.

Key concepts

Natural Selection

Natural selection is one of the core principles of evolutionary biology. It is the process by which certain traits become more or less common in a population due to the reproductive success of organisms. It operates on the principle that individuals with favorable traits that are well-suited to their environment tend to survive longer and produce more offspring, passing on these advantageous traits to future generations.

For example, consider a species of birds where those with longer beaks can reach food more efficiently. Over time, long-beaked birds may dominate the population as they are able to eat and survive better than their short-beaked counterparts. This is natural selection at work—favoring the trait of a longer beak.

An essential aspect of natural selection is that it acts on existing variations within a population. These variations arise due to random mutations, which may then be sorted by natural selection based on how they affect an organism's ability to survive and reproduce.

Genetic Drift

Genetic drift is a phenomenon that causes random changes in allele frequencies within a population. It is particularly significant in small populations where random events can have a larger impact on the genetic composition of the group.

Consider the tossing of a coin. If you toss it a hundred times, the results should approximately be 50% heads and 50% tails. However, toss it just a few times, and the ratio could be skewed due to chance. Similarly, in small populations, alleles can become more or less common simply by chance. A natural disaster, for instance, could randomly eliminate individuals with certain alleles, changing the gene pool composition even if those alleles gave no advantage or disadvantage.

Genetic drift can lead to significant changes over time and can sometimes cause rare alleles to become fixed (present in all individuals in a population) or lost entirely.

Gene Flow

Gene flow, also known as gene migration, refers to the transfer of genetic material between separate populations. This can occur when organisms move from one habitat to another, or through mechanisms such as pollen being carried to a new location by wind or animals.

Gene flow can have a considerable effect on the genetic diversity of a population. Take the Galápagos medium ground finches as an example. When individuals fly from one island to another, they may mate with the local population, introducing new alleles. This genetic mixing can increase the diversity within populations, potentially introducing traits that could be beneficial in different environmental contexts.

Gene flow can counteract the effects of natural selection and genetic drift by preventing populations from becoming too genetically different, potentially reducing the chances of speciation, the process by which new species are formed.

Mutation

A mutation is a change in the DNA sequence that can lead to a change in the gene. Mutations are the source of genetic diversity, providing the raw material upon which the other mechanisms of evolution, such as natural selection, can act.

Mutations can occur spontaneously during DNA replication or as a result of environmental factors like radiation or chemicals. While most mutations have no effect or are harmful, some may confer an advantage to an organism. A single mutation can potentially have a large effect, but most evolutionary change is the result of the accumulation of many mutations over time.

To illustrate, if a mutation leads to a new beneficial trait, such as resistance to a specific disease, the individuals carrying this trait could have a higher chance of surviving and reproducing. Over time, the frequency of this advantageous mutation could increase within the population, illustrating the role of mutations in evolutionary processes.