What is a genetic drift?

• A. A systematic change in phenotype
• B. A change in allele frequency due to random sampling in a population
• C. Natural selection
• D. Mutation in DNA sequence

Answer: (B)

Genetic drift refers to a change in allele frequencies within a population due to random sampling effects, particularly in small populations. This phenomenon occurs by chance rather than by selection pressures and can lead to significant changes over time, such as the loss of genetic variation or the fixation of alleles, regardless of their adaptive value. Unlike natural selection, which relates to an organism's ability to survive and reproduce based on advantageous traits, genetic drift is random and does not necessarily favor any particular trait.

In a population, if a few individuals randomly contribute disproportionately to the next generation's gene pool, their alleles will be overrepresented relative to others. This random fluctuation can lead to differing allele frequencies in different populations, contributing to evolutionary divergence.

The other answer choices involve different concepts in genetics and evolution. A systematic change in phenotype pertains to non-random processes such as selection, while natural selection is an adaptive process driven by environmental pressures. Mutation refers to changes at the DNA level, which introduce new genetic variations but do not inherently involve the random changes in allele frequencies characteristic of genetic drift.