In which phase of meiosis does crossing over occur?

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

Answer: (B)

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. Recognize that crossing over is a crucial event in meiosis that increases genetic diversity. It involves the exchange of genetic material between homologous chromosomes.
3. Identify the phases of meiosis I: Prophase I, Metaphase I, Anaphase I, and Telophase I. Each phase has distinct characteristics and roles in the process.
4. Focus on Prophase I, where homologous chromosomes pair up in a process called synapsis. This is the stage where crossing over occurs, facilitated by the formation of chiasmata, which are the points of contact between homologous chromosomes.
5. Note that crossing over does not occur in Metaphase I, Anaphase I, or Telophase I. These phases are involved in aligning chromosomes at the metaphase plate, separating homologous chromosomes, and completing the division, respectively.