Problem 25 - Objective Biology for NEET

Question

Anaphase is characterized by (a) Splitting of centromere (b) Separation of chromatids (c) Movement of chromatid to opposite pole (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) All of these.

Step 1: Understanding Anaphase

Anaphase is a phase in the cell cycle, particularly in mitosis and meiosis, where the chromosomes split and the sister chromatids move to opposite poles of the cell.

Step 2: Analyzing the Options

(a) Splitting of centromere - This happens in anaphase as centromeres split allowing the sister chromatids to separate. \n (b) Separation of chromatids - This is an event that characterizes anaphase. The sister chromatids of each chromosome are pulled apart and move towards the opposite poles of the cell. \n (c) Movement of chromatid to opposite pole - This is an event in anaphase where the split chromatids are pulled along the spindle network to opposite sides of the cell. \nFrom these observations, all options provided seem to be events that occur in anaphase.

Step 3: Concluding the Analysis

Considering the definitions and processes involved, it can be concluded that option (d) is the correct answer as it states all characteristics given are indeed happening during anaphase.

Key Concepts

Cell Cycle

The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. It's structured in distinct phases: G1 (gap 1, cell growth), S (synthesis, DNA replication), G2 (gap 2, preparation for mitosis), and M (mitosis or meiosis, depending on the cell type). Each phase is crucial for proper cell division, ensuring that the genetic material is accurately copied and distributed to the daughter cells.

The M phase is particularly critical, which is where mitosis and meiosis occur, and as our exercise highlights, includes steps like prophase, metaphase, anaphase, and telophase. Anaphase plays a key role in M phase as it ensures each new cell will receive an identical set of chromosomes.

Mitosis

Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth. Mitosis consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase.

During anaphase, which is our focus, sister chromatids, previously attached at the centromere, are separated and pulled to opposite poles of the cell. This separation ensures that each new daughter cell will have a complete set of chromosomes. Anaphase is characterized by the rapid movement of chromatids, facilitated by the spindle fibers.

Meiosis

Meiosis, on the other hand, is a specialized type of cell division that reduces the chromosome number by half, resulting in the production of four daughter cells, each with half of the number of chromosomes of the parent cell. This process is essential for sexual reproduction and occurs in two rounds of division: meiosis I and meiosis II.

Anaphase in meiosis is similar to that in mitosis in that chromosomes move to the poles of the cell; however, there are key differences. In meiosis I, homologous chromosomes are separated, while in meiosis II, which is similar to mitosis, sister chromatids are separated. These steps are vital for genetic diversity and accurate segregation of chromosomes.

Chromatids

Chromatids are one of two identical halves of a replicated chromosome, which are joined together by a single centromere before a cell divides. When a chromosome is replicated during the S phase of the cell cycle, it consists of two chromatids, known as sister chromatids.

In anaphase of mitosis and meiosis II, the centromeres split, and the spindle fibers pull the sister chromatids apart to opposite poles of the cell, after which they are considered individual chromosomes. This separation is a central aspect of cell division and is essential for the equal distribution of genetic material.

Centromere

The centromere is the region of a chromosome to which the microtubules of the spindle attach, via a protein complex called the kinetochore, during cell division.

During anaphase, the centromeres play a critical role as they split, allowing the sister chromatids to move to opposite ends of the cell. The centrality of the centromere in cell division makes it a key player in genetics and cell biology. Disruptions in centromere function can result in aneuploidy, a condition where cells have an abnormal number of chromosomes, which can lead to various diseases.

Spindle Fibers

Spindle fibers are composed of microtubules and proteins that form a spindle shape and are essential for moving chromosomes during cell division.

They extend from the centrosomes at opposite poles of the cell and attach to the kinetochore in the centromere region of each chromosome. During anaphase, the spindle fibers shorten, which pulls the sister chromatids apart to opposite poles of the cell. The dynamic rearrangement of the spindle fibers is key to the successful completion of cell division and the accurate distribution of chromosomes to daughter cells.