In the eukaryotic cell cycle, which phase must occur before meiosis I can begin?

• A. G2 phase of interphase (cell growth and preparation for division)
• B. Prophase I (homologous chromosomes pair and crossing over occurs)
• C. S phase of interphase (DNA replication)
• D. Cytokinesis (division of the cytoplasm)

Answer: (C)

Verified step by step guidance

1. Understand the sequence of phases in the eukaryotic cell cycle: G1 phase, S phase, G2 phase, followed by meiosis or mitosis.
2. Recall that the S phase is when DNA replication occurs, doubling the genetic material to prepare for cell division.
3. Recognize that meiosis I requires replicated chromosomes (each consisting of two sister chromatids) to properly pair and undergo recombination.
4. Identify that Prophase I is the first stage of meiosis I itself, where homologous chromosomes pair and crossing over happens, so it cannot occur before meiosis I begins.
5. Conclude that the S phase of interphase must occur before meiosis I to ensure the DNA is replicated and ready for the subsequent steps of meiosis.