In population genetics, which of the following processes directly produces gene flow by moving alleles from one population to another?

Introduction / Context:
Evolutionary biology explains how allele frequencies change within populations over time. Several mechanisms contribute to these changes, including natural selection, genetic drift, mutation, and gene flow. This question focuses specifically on gene flow, which is the transfer of alleles between populations, and asks which process directly causes that movement of alleles from one population to another.

Given Data / Assumptions:

• Populations can exchange individuals and alleles under certain conditions.
• Gene flow involves the movement of alleles into or out of a population.
• Several evolutionary forces are listed: movement of individuals, genetic drift, mutation, and artificial selection.
• The question requires identifying the process that directly produces gene flow.

Concept / Approach:
Gene flow occurs when individuals or their gametes move between populations and successfully reproduce, introducing new alleles or changing the frequency of existing ones. When individuals migrate and breed, their alleles mix with the gene pool of the new population. Genetic drift refers to random changes in allele frequencies within a population due to chance events, not movement between populations. Mutation creates new alleles within a population, and artificial selection changes allele frequencies through human choice, but neither of these processes by itself involves migration between populations. Thus, the correct approach is to link gene flow with migration or movement of individuals or gametes.

Step-by-Step Solution:
Step 1: Recall the definition of gene flow as the movement of alleles between populations. Step 2: Recognize that gene flow happens when individuals migrate into or out of populations and successfully reproduce there. Step 3: Identify which option describes such migration or movement of individuals. Step 4: Option A, individuals moving into a population, clearly describes immigration and potential interbreeding with the resident population. Step 5: Confirm that the other listed mechanisms do not directly involve movement of individuals between populations and therefore do not define gene flow.

Verification / Alternative check:
Textbook diagrams of gene flow often show arrows representing individuals moving from one population to another, carrying alleles with them. Classic examples include pollen carried by wind between plant populations or animals migrating between separated groups. In these examples, it is the movement and subsequent reproduction of individuals that changes the allele frequencies between populations, which matches option A. Genetic drift and mutation are typically shown as internal processes operating within a single population, while artificial selection is driven by human choice rather than movement between populations.

Why Other Options Are Wrong:
Option B (Genetic drift): This is random change in allele frequencies due to sampling effects in small populations. It does not necessarily involve movement of individuals between populations.
Option C (Mutation): Mutation introduces new alleles into the gene pool, but it acts within a single population and does not by itself cause movement of alleles between populations.
Option D (Artificial selection): This is human directed selection for certain traits, such as breeding of crops or animals, which changes allele frequencies through selection rather than migration.

Common Pitfalls:
Students sometimes confuse all evolutionary forces and treat them as interchangeable. Another pitfall is to think that any change in allele frequencies equals gene flow. While all these processes can change allele frequencies, only gene flow specifically refers to movement between populations. Confusing mutation and gene flow is also common, but mutation is a source of new variation, whereas gene flow redistributes existing variation between groups.

Final Answer:
Gene flow is most directly caused when individuals move into a population and contribute their alleles to that population’s gene pool.