Crossing over (homologous recombination) occurs during which phase of meiosis?

• A. Anaphase I
• B. Prophase II
• C. Metaphase I
• D. Prophase I (specifically during pachytene)

Answer: (D)

Verified step by step guidance

1. Recall the stages of meiosis I and meiosis II, focusing on the events that characterize each phase.
2. Understand that crossing over, or homologous recombination, involves the exchange of genetic material between homologous chromosomes.
3. Identify that homologous chromosomes pair up and form synaptonemal complexes during Prophase I, which facilitates crossing over.
4. Recognize that crossing over specifically occurs during the pachytene substage of Prophase I, when the chromosomes are fully synapsed.
5. Conclude that crossing over does not occur during Anaphase I, Metaphase I, or Prophase II, but specifically during Prophase I.