Which of the phases of cell cycle is of longest duration ?

Options

A. Leptotene
B. Zygotene
C. Pachytene
D. Diplotene

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Cell Cycle**: The cell cycle consists of several phases, including interphase and mitotic phases. In the context of meiosis, particularly meiosis I, prophase I is divided into several stages.

2. **Identifying the Stages of Prophase I**: Prophase I of meiosis includes five stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis. Each of these stages has distinct characteristics and durations.

3. **Analyzing Each Stage**:
- **Leptotene**: This is the first stage where the chromosomes begin to condense. It is of shorter duration.
- **Zygotene**: In this stage, chromosomes start pairing, and the synaptonemal complex forms. This stage is also of shorter duration.
- **Pachytene**: Here, bivalent chromosomes or tetrads form, and crossing over occurs, leading to genetic recombination. This stage is longer than the previous two but not the longest.
- **Diplotene**: In this stage, the synaptonemal complex dissolves, and chiasmata (X-shaped structures) appear due to crossing over. This stage is known to be the longest phase of prophase I and can last for extended periods, especially in oocytes of some vertebrates.

4. **Conclusion**: Among the stages of prophase I, Diplotene is identified as the longest duration phase.

5. **Final Answer**: The phase of the cell cycle that is of longest duration is **Diplotene**.

---