The nucleus __ during prophase II.
The Correct Answer and Explanation is:
The correct answer to complete the statement is:
The nucleus disappears during prophase II. In Metaphase II, the chromosomes line up single file down the middle of the cell. In Anaphase II, the sister chromatids split up.
Explanation:
Mitosis and meiosis are two types of cell division processes, with meiosis consisting of two stages: Meiosis I and Meiosis II. The question refers to events that occur during Meiosis II, which is similar to mitosis but involves the division of haploid cells, ultimately resulting in four non-identical haploid gametes.
- Prophase II:
- In Meiosis II, prophase II marks the beginning of the second division. During this phase, the nuclear envelope disappears, allowing the spindle fibers to form and attach to the centromeres of chromosomes. The chromosomes, each consisting of two sister chromatids, become visible under the microscope. This is similar to prophase in mitosis, where the nuclear membrane also breaks down. However, in Meiosis II, the cells are already haploid (with half the number of chromosomes), which means each chromosome is still in its duplicated form (two sister chromatids attached).
- Metaphase II:
- In Metaphase II, the chromosomes line up single file along the middle (equator) of the cell, just like in metaphase of mitosis. The alignment of chromosomes at the cell’s center is critical for ensuring that each daughter cell receives an equal and accurate set of chromosomes. Unlike Metaphase I in Meiosis I, where homologous chromosomes pair up, in Metaphase II, it is individual chromosomes that align, each chromosome still having two sister chromatids attached by a centromere.
- Anaphase II:
- In Anaphase II, the sister chromatids separate and are pulled toward opposite poles of the cell by the spindle fibers. This is the key event that ensures each daughter cell will receive one copy of each chromosome, reducing the chromosome number from haploid to two sets in the final telophase.
Finally, Meiosis II culminates in Telophase II, where the nuclear envelope reforms around the separated chromatids, and cytokinesis occurs, resulting in four non-identical haploid daughter cells. This reduction in chromosome number ensures genetic diversity among the resulting gametes.