USA Biology Olympiad (USABO) Practice Exam

What is the impact of sexual processes, such as meiosis and fertilization, on allele frequencies within a population?

1. They increase allele frequencies.

2. They decrease allele frequencies.

3. They have no direct effect.

4. They may alter observed frequencies.

The correct answer is: They have no direct effect.

The correct answer focuses on how sexual processes, specifically meiosis and fertilization, interact with the genetic makeup of a population. Meiosis involves the production of gametes (sperm and eggs) through a reduction division, ensuring that these gametes carry only one allele from each gene pair. This process introduces genetic variation by shuffling alleles through crossing over and independent assortment. Fertilization then combines these gametes from two parents, further enhancing the genetic diversity of the offspring. While these processes play a crucial role in generating new genetic combinations, they do not directly influence the overall allele frequencies within a population in isolation. Instead, the impact on allele frequencies is more accurately seen over generations and influenced by additional factors such as natural selection, genetic drift, and migration. Therefore, one can understand that rather than having a direct effect, sexual processes create the variability upon which evolutionary forces act to change allele frequencies over time. The other options suggest that there is a definitive increase or decrease in allele frequencies or that there is an immediate effect, which does not capture the complexity of how sexual reproduction adds variation upon which other mechanisms work. Recognizing that sexual processes generate genetic diversity but do not directly change allele frequencies is key to understanding population genetics.