During which stage of meiosis does crossing over, which increases genetic diversity, occur?

• A. Metaphase I
• B. Prophase I
• C. Telophase II
• D. Interphase

Answer: (B)

Crossing over occurs during Prophase I of meiosis. This is a crucial stage where homologous chromosomes come together to form tetrads, or pairs of homologous chromosomes. During this pairing, exchange of genetic material can occur between non-sister chromatids, resulting in new combinations of alleles. This process not only increases genetic diversity but also ensures that the resulting gametes (sperm and eggs) have a unique genetic makeup. The significance of crossing over is highlighted in the context of evolution and natural selection, as it contributes to variation within a population.

In contrast, the other stages mentioned do not involve crossing over. Metaphase I is characterized by the alignment of tetrads at the equatorial plane of the cell; Telophase II involves the separation of sister chromatids and the formation of nuclear membranes around the newly formed cells; and Interphase is a phase of the cell cycle where the cell prepares for division but does not itself involve the actual meiotic processes. Thus, Prophase I is distinctly where the critical event of crossing over takes place.