The effects of genetic drift are more marked in

Options

A. larger populations
B. Mendelian populations
C. island populations
D. smaller populations.

Explanation

**Step-by-Step Solution:**

1. **Understanding Genetic Drift**: Genetic drift refers to the random changes in allele frequencies within a population due to chance events. It can lead to significant changes in small populations where the loss of individuals can drastically alter the genetic makeup.

2. **Hardy-Weinberg Equilibrium**: In a stable population, the allele frequencies remain constant over generations, a state known as Hardy-Weinberg equilibrium. Genetic drift disrupts this equilibrium by causing fluctuations in allele frequencies.

3. **Example of Genetic Drift**: Consider a small population of beetles with two color alleles (P for blue and Q for red). If a random event (like a natural disaster) kills a significant number of beetles, the remaining population may have a drastically different allele frequency than before.

4. **Impact of Population Size**: In small populations, the loss of even a few individuals can lead to a significant change in allele frequencies. For example, if there are 10 beetles (5 blue and 5 red) and a random event kills 4 blue beetles, the frequency of the blue allele drops dramatically. In contrast, in a larger population, the same event would have a negligible effect on overall allele frequencies.

5. **Conclusion**: The effects of genetic drift are more pronounced in smaller populations because random events can lead to significant changes in allele frequencies, disturbing the Hardy-Weinberg equilibrium. Therefore, the correct answer is that genetic drift is more marked in smaller populations.

**Final Answer**: The effects of genetic drift are more marked in smaller populations.

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