Problem 129 - Objective Biology for NEET

Question

Assertion: Chromatid separation occurs in anaphase stage. Reason: Centromere splitting occurs in anaphase stage.

Step-by-Step Solution

Answer

The assertion and the reasoning are correct. Chromatid separation and centromere splitting occur in the anaphase stage of cell division.

Step 1: Understand Chromatid Separation and Centromere Splitting

During cell division or mitosis, chromatids are separated and pulled towards opposite ends of the cell. This is facilitated by the splitting of the centromere, the point at which the chromatids are attached.

Step 2: Identify the Phase

Anaphase is one of the stages of mitosis. This is a significant stage in cell division because it is during this phase that the chromatids separate and move to opposite ends of the cell. This is facilitated by the splitting of the centromere.

Step 3: Assert the Statements

Given the understanding of the process of cell division, it can be stated that both the assertion and the reason are correct. Both the chromatid separation and the centromere splitting occur during the anaphase stage of cell division.

Key Concepts

Chromatid Separation

During anaphase, a crucial step in cell division known as mitosis, chromatids separate. Each chromosome consists of two sister chromatids, which are identical copies of DNA. These chromatids are held together by structures called centromeres. At the start of anaphase, the chromatids detach and are pulled toward opposite poles of the cell.
This movement is critical because it ensures that each new daughter cell receives an identical set of chromosomes. By distributing the chromatids equally, anaphase ensures genetic continuity from one cell generation to the next.

Centromere Splitting

Centromere splitting is an essential event that facilitates the separation of chromatids. Prior to anaphase, the centromeres keep the sister chromatids tethered together. This connection holds the duplicate genetic material intact until it's time to divide.
During anaphase, enzymes known as separases cut the centromere's cohesins, proteins that hold the chromatids together. This cutting action

• releases the chromatids, allowing them to be pulled apart,
• marks the exact moment when the chromatids become individual chromosomes,
• ensures each future cell nucleus receives the right number of chromosomes.

Mitosis

Mitosis is a highly-regulated process through which cells divide to produce identical daughter cells. It encompasses several phases, including interphase, prophase, metaphase, anaphase, and telophase.
One of the primary purposes of mitosis is to ensure genetic information is accurately passed from parent to daughter cells. Notably, anaphase is pivotal in mitosis because it involves the

• chromatid separation, driven by centromere splitting,
• automated pull of chromatids to opposite sides,
• foundation for equal chromosome distribution.

This precision in distributing chromosomes is fundamental for keeping genetic integrity intact across human cells.

Cell Division

Cell division encompasses both mitosis and cytokinesis, the latter being the process of cytoplasm division. Together, they form the basis for biological growth and consistency.
This process is not only central to

• organism growth,
• tissue repair,
• asexual reproduction in certain species.

Cell division initiates with the duplication of the cell's entire set of genes through DNA replication during interphase. The subsequent phases of mitosis, especially anaphase, ensure that these genes are equally apportioned. Post mitosis, cytokinesis concludes cell division by physically dividing the cytoplasm, resulting in two distinct cells.