During which stage of meiosis does crossing-over occur?

• A. Metaphase I
• B. Anaphase I
• C. Telophase I
• D. Prophase I

Answer: (D)

Verified step by step guidance

1. Understand the process of meiosis, which is a type of cell division that reduces the chromosome number by half, creating four haploid cells. It consists of two consecutive divisions: meiosis I and meiosis II.
2. Learn about the stages of meiosis I: Prophase I, Metaphase I, Anaphase I, and Telophase I. Each stage has distinct events that contribute to genetic diversity and reduction of chromosome number.
3. Focus on Prophase I, where homologous chromosomes pair up in a process called synapsis. This pairing forms structures known as tetrads, which are crucial for genetic recombination.
4. Recognize that crossing-over occurs during Prophase I. This is the exchange of genetic material between non-sister chromatids of homologous chromosomes, leading to genetic variation in the resulting gametes.
5. Remember that crossing-over is facilitated by the formation of chiasmata, which are the visible manifestations of crossover events. This process is essential for increasing genetic diversity in sexually reproducing organisms.