Which phase’s intiation is indicated by the appearance of the chromosomes as thin threads in the nucleus?

The correct answer is: A. Prophase

Prophase is the first phase of mitosis. It is characterized by the following events:

• Condensation of chromosomes: The chromosomes condense from long, thin threads into short, thick rods.
• Disappearance of the nuclear envelope: The nuclear envelope breaks down, releasing the chromosomes into the cytoplasm.
• Formation of the mitotic spindle: The mitotic spindle is a structure that helps to move the chromosomes during mitosis. It is composed of microtubules that radiate from the centrosomes.
• Attachment of the chromosomes to the mitotic spindle: The chromosomes attach to the mitotic spindle at their centromeres.

The appearance of the chromosomes as thin threads in the nucleus indicates the initiation of prophase. This is because the chromosomes condense during prophase, which makes them visible under a microscope.

The other options are incorrect because they do not describe the events that occur during prophase.

• Metaphase is the second phase of mitosis. During metaphase, the chromosomes line up at the equator of the cell.
• Anaphase is the third phase of mitosis. During anaphase, the sister chromatids of each chromosome are separated and pulled to opposite poles of the cell.
• Telophase is the fourth and final phase of mitosis. During telophase, the chromosomes decondense and the nuclear envelope reforms. The mitotic spindle also disappears.