Problem 68 - Objective Biology for NEET

Question

Mitotic anaphase differs from metaphase in possessing (a) Same number of chromosomes and half number of chromatids. (b) Half the number of chromosomes and same number of chromatids. (c) Half the number of chromosomes and half number of chromatids. (d) Same number of chromosomes and same number of chromatids.

Step-by-Step Solution

Answer

The correct answer is (a): Anaphase has the same number of chromosomes and half the number of chromatids compared to Metaphase.

Step 1: Understanding Mitosis

Mitosis is a method of cell division, where a single cell divides into two identical daughter cells. Mitosis has various stages such as Prophase, Prometaphase, Metaphase, Anaphase and Telophase.

Step 2: Understanding Metaphase

At the Metaphase, chromosomes align at the metaphase plate (the equatorial plane) and are at peak condensation. Each chromosome has two sister chromatids, which are duplicates of each other.

Step 3: Understanding Anaphase

During Anaphase, paired sister chromatids separate and move to opposite ends of the cell. This gives rise to two independent chromosomes.

Step 4: Determine Differences

When comparing Metaphase to Anaphase, the Anaphase has the same number of chromosomes as Metaphase (since each sister chromatid is considered a chromosome post separation), but there is a halving in chromatid number, since the paired chromatids have separated.

Key Concepts

Mitosis Stages

Mitosis is a crucial process in which a single cell divides to create two identical daughter cells. It is a complex event divided into distinct stages: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase. Each of these stages is characterized by specific events and milestones. During Prophase, chromatin fibers condense into visible chromosomes, and the nuclear envelope begins to break down. Prometaphase sees the creation of the spindle apparatus and the connection of spindle fibers to chromosomes. Metaphase follows, characterized by the alignment of chromosomes along the metaphase plate.

After Metaphase, the cell progresses to Anaphase, a stage marked by the separation of sister chromatids. Finally, in Telophase, the separated chromatids, now chromosomes, arrive at opposite poles, and new nuclear membranes form around them. It is essential to understand these stages as they ensure genetic material is accurately distributed, with each new daughter cell receiving an identical set of chromosomes.

Chromosome Alignment

Chromosome alignment is a pivotal moment in mitosis, particularly during Metaphase. This stage is characterized by all chromosomes aligning at the metaphase plate, an imaginary plane equidistant between the cell's poles. This precise alignment is crucial for the next phase of mitosis, Anaphase. The alignment is aided by the mitotic spindle, a structure composed of microtubules, which play a role in moving chromosomes. Each chromosome's kinetochores, protein complexes at the centromere region, attach to the spindle fibers, ensuring that each sister chromatid will move to opposite poles of the cell when they separate.

For the cell to maintain genetic consistency, this alignment must be perfect. If a chromosome does not align correctly, it could lead to an unequal distribution of chromosomes during cell division, potentially causing genetic disorders. Hence, the precision of chromosome alignment is a testament to the cell's intricate mechanisms for preserving genetic information.

Sister Chromatid Separation

The separation of sister chromatids signifies the transition from Metaphase to Anaphase in mitosis and is a defining moment in the process of cell division. Sister chromatids are essentially identical copies of a chromosome, held together by a structure called the centromere. During Anaphase, enzymes break down proteins that hold the sister chromatids together, allowing them to move apart.

Once separated, each chromatid becomes an independent chromosome. The segregation is facilitated by the mitotic spindle's microtubules, which pull the chromosomes toward the opposite poles of the cell. This step is critical because it ensures that each new daughter cell will have the same number and type of chromosomes as the original parent cell. Any errors in the separation process could lead to an unequal share of genetic material, resulting in disorders or cell death. This step's successful completion sets the stage for the final phase of mitosis, where two new nuclei form around the separated chromosomes, leading to the birth of two genetically identical cells.