What is one major effect of genetic drift on a population's genetic diversity?

Genetic drift is a process that causes random changes in the allele frequencies of a population, particularly in small populations. One major effect of genetic drift is that it tends to reduce genetic diversity within a population. This occurs because the random nature of genetic drift can lead to certain alleles becoming fixed—meaning that they reach a frequency of 100% in the population—while others may be lost entirely.

When alleles are lost through genetic drift, the overall genetic variation decreases, which can limit the population's ability to adapt to environmental changes. This reduction in genetic diversity can have significant long-term consequences for the population, making it more vulnerable to diseases, environmental changes, and other factors that could threaten its survival. Thus, the correct answer reflects the impact of genetic drift on decreasing genetic variability in populations.