There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation most likely resulted from
a. Genetic drift.
b. Gene flow.
c. Nonrandom mating.
d. Directional selection.

Verified step by step guidance

1. Understand the genotypes present in each population: Population 1 consists entirely of individuals with genotype AA, while Population 2 consists entirely of individuals with genotype aa.
2. Consider the concept of genetic drift: Genetic drift refers to random changes in allele frequencies in a population, which is more pronounced in small populations. However, since both populations are fixed for different alleles (AA and aa), genetic drift is unlikely to be the cause of the observed genetic variation.
3. Evaluate the possibility of gene flow: Gene flow involves the transfer of alleles between populations. Given that the populations are located far from each other, gene flow is unlikely to occur, as there is no exchange of individuals or alleles between the populations.
4. Analyze the role of nonrandom mating: Nonrandom mating affects genotype frequencies but not allele frequencies. Since both populations are fixed for different alleles, nonrandom mating is not a contributing factor to the observed genetic variation.
5. Consider directional selection: Directional selection favors one allele over another, leading to changes in allele frequencies. However, since both populations are fixed for different alleles and the environmental conditions are similar, directional selection is unlikely to be responsible for the observed genetic variation.

Key Concepts

Genetic Drift

Genetic drift refers to random changes in allele frequencies within a population, often having a more pronounced effect in small populations. It can lead to the loss or fixation of alleles over time, independent of natural selection. In isolated populations, genetic drift can significantly impact genetic variation, especially when population sizes are small.

Gene Flow

Gene flow is the transfer of genetic material between separate populations, often through migration. It can introduce new alleles into a population, increasing genetic diversity and potentially altering allele frequencies. In the context of isolated populations, gene flow is unlikely unless individuals from different populations interbreed, which is not the case here.

Directional Selection

Directional selection is a form of natural selection where one extreme phenotype is favored over others, leading to a shift in allele frequencies in a particular direction. This process can result in the predominance of certain traits within a population. However, in the given scenario, the environmental conditions are similar, making directional selection an unlikely cause of genetic variation.