In meiosis, how does prophase I differ from prophase II?

• A. Spindle fibers do not form during prophase I, but they do during prophase II.
• B. The nuclear envelope remains intact during prophase I, but breaks down during prophase II.
• C. Chromosome replication occurs during prophase I, but not during prophase II.
• D. Homologous chromosomes pair and undergo crossing over during prophase I, but not during prophase II.

Answer: (D)

Verified step by step guidance

1. Understand that meiosis consists of two successive divisions: meiosis I and meiosis II, each with its own prophase stage (prophase I and prophase II).
2. Recall that during prophase I, homologous chromosomes pair up in a process called synapsis, forming tetrads, and exchange genetic material through crossing over, which increases genetic diversity.
3. Note that during prophase II, the cells have already undergone one division, so homologous chromosomes are no longer paired; instead, individual chromosomes prepare for the second division without crossing over.
4. Recognize that spindle fibers form in both prophase I and prophase II to help separate chromosomes, so the presence or absence of spindle fibers is not a distinguishing feature between these stages.
5. Remember that chromosome replication occurs before meiosis begins, during the S phase of interphase, so no replication happens during either prophase I or prophase II.