What effect does natural selection have on allele frequencies?

Natural selection significantly alters allele frequencies within a population by favoring certain alleles over others based on their contribution to the reproductive success of individuals. This process occurs as individuals with advantageous traits—often driven by environmental factors—are more likely to survive and reproduce, passing those beneficial alleles to their offspring. As these favored alleles increase in frequency over generations, the overall genetic makeup of the population shifts, leading to evolution.

In contrast, the other options do not accurately capture the dynamic nature of natural selection. For instance, stating that it has no effect ignores the foundational principle of evolution through natural selection. Saying it maintains allele frequencies is misleading, as natural selection actively promotes change rather than stability. Finally, the assertion that it increases genetic variation does not align with the process; while natural selection can sometimes act on existing variation, it often leads to a reduction in genetic variation as certain alleles become predominant in the population. Thus, the key impact of natural selection is its capability to significantly alter which alleles are prevalent over time.