Which character marks the beginning of the second phase of mitosis ?

Options

A. Appearance of chromosomes
B. Initiation of spindle
C. Disintegration of nuclear envelope
D. Formation of equatorial plate

Answer

To solve the question "Which character marks the beginning of the second phase of mitosis?", we need to understand the phases of mitosis and what occurs at the beginning of each phase.

### Step-by-Step Solution:

1. **Understand Mitosis Phases**: Mitosis consists of four main phases: prophase, metaphase, anaphase, and telophase. The question specifically asks about the beginning of the second phase, which is metaphase.

2. **Identify Characteristics of Prophase**: In prophase, the chromosomes condense and become visible under a microscope. The nuclear envelope begins to break down, and the mitotic spindle starts to form.

3. **Transition to Metaphase**: The transition from prophase to metaphase is marked by the complete disintegration of the nuclear envelope. This allows the chromosomes to align at the cell's equatorial plane.

4. **Characteristics of Metaphase**: During metaphase, the chromosomes are fully condensed and aligned at the metaphase plate, and the spindle fibers attach to the centromeres of the chromosomes.

5. **Conclusion**: Since the question asks for the characteristic that marks the beginning of metaphase, the correct answer is the disintegration of the nuclear envelope.

### Final Answer:
The characteristic that marks the beginning of the second phase of mitosis (metaphase) is **disintegration of the nuclear envelope**.