USA Biology Olympiad (USABO) Practice Exam

What factor could lead to increased genetic variation in populations?

1. Gene mutation rates being reduced

2. Crossing over during meiosis

3. Isolation from other populations

4. Stable environmental conditions

The correct answer is: Crossing over during meiosis

Increased genetic variation in populations is significantly influenced by the process of crossing over during meiosis. This biological mechanism occurs during the formation of gametes when homologous chromosomes exchange genetic material. As a result, the alleles on chromosomes are shuffled, leading to new combinations of genes that were not present in either parent. This recombination introduces diversity within the gene pool, fostering variation among offspring. Additionally, it is essential to understand how the other factors do not contribute to increased genetic variation in the same way. For instance, reduced gene mutation rates would limit the introduction of new genetic variants, while isolation from other populations could lead to inbreeding and reduced genetic diversity over time. Similarly, stable environmental conditions might not necessarily drive variation; rather, it is often the presence of fluctuating environments that selects for diverse traits and allows variation to thrive. Thus, crossing over during meiosis emerges as a key mechanism for enhancing genetic variability in populations.