In which phase of mitosis would chromosomes line up at the centre of the spindle:
A. anaphase
B. interphase
C. prophase
D. metaphase
The correct answer and explanation is :
The correct answer is D. metaphase.
Explanation:
Mitosis is a type of cell division that results in two identical daughter cells. It is divided into several stages: prophase, metaphase, anaphase, and telophase. Each of these phases plays a critical role in ensuring that the genetic material is properly distributed between the daughter cells.
In metaphase, the chromosomes align at the center of the spindle apparatus, which is also referred to as the metaphase plate. The spindle apparatus consists of microtubules that extend from the centrosomes at opposite poles of the cell. These microtubules attach to the centromeres of the chromosomes, which are the regions where the two sister chromatids (replicated chromosomes) are held together.
During metaphase, the chromosomes are fully condensed and aligned in a single plane, ensuring that they are in the correct position for the next stage of mitosis. This alignment is essential for ensuring that each daughter cell receives an identical set of chromosomes.
This stage is crucial for maintaining genomic stability because improper alignment can lead to errors during chromosome separation, potentially resulting in aneuploidy (the condition of having an abnormal number of chromosomes), which can cause diseases like cancer.
Let’s briefly review the other phases of mitosis to provide further clarity:
- Prophase: This is the first stage of mitosis, where chromosomes become visible as they condense, and the nuclear envelope begins to break down. The mitotic spindle also starts to form, but the chromosomes are not yet aligned in the center.
- Anaphase: In this phase, the sister chromatids are pulled apart toward opposite poles of the cell. The chromosomes are no longer aligned at the center.
- Interphase: This is not a stage of mitosis but a phase that precedes mitosis. Interphase consists of three sub-phases (G1, S, and G2) during which the cell grows, DNA is replicated, and preparation for mitosis occurs.
Thus, metaphase is the only phase where chromosomes line up at the center of the spindle.