One event occurring during prophase is __. ANSWER Unselected cytokinesis Unselected the alignment of chromosomes in a single plane Unselected the synthesis of a new nuclear envelope Unselected the beginning of the formation of a mitotic spindle Unselected separation of sister chromatids
The Correct Answer and Explanation is:
The correct answer is the beginning of the formation of a mitotic spindle.
Explanation:
Prophase is the first stage of mitosis, the process by which a eukaryotic cell divides into two identical daughter cells. During this phase, several key events take place, preparing the cell for the subsequent stages of mitosis (metaphase, anaphase, and telophase).
- Chromosome Condensation: Chromosomes, which were previously in a less condensed, thread-like form (chromatin), begin to condense into visible structures. Each chromosome consists of two sister chromatids held together at a region called the centromere.
- Mitotic Spindle Formation: One of the most critical events of prophase is the beginning of the formation of the mitotic spindle. This structure is made up of microtubules and is responsible for organizing and segregating the chromosomes during cell division. The spindle fibers emanate from two structures called the centrosomes, which move toward opposite poles of the cell.
- Nuclear Envelope Breakdown: As prophase progresses, the nuclear envelope starts to break down, allowing the spindle fibers to interact with the chromosomes. This event is crucial for ensuring that the chromosomes can align properly in the following stage, metaphase.
- Nucleolus Disappears: The nucleolus, which is the site of ribosome production in the nucleus, also disappears during prophase. This step is part of the general breakdown of the cell’s internal structure to facilitate the separation of genetic material.
Regarding the other options:
- Cytokinesis occurs after mitosis (during telophase) and involves the division of the cytoplasm.
- The alignment of chromosomes happens during metaphase, not prophase.
- The synthesis of a new nuclear envelope happens later in telophase.
- The separation of sister chromatids happens during anaphase.
Thus, the formation of the mitotic spindle is the key event that begins during prophase.
