Problem 63 - Objective Biology for NEET

Question

The best stage to observe the shape, size and number of chromosomes is (a) Interphase (b) Metaphase (c) Prophase (d) Telophase

Step-by-Step Solution

Answer

The best stage to observe the shape, size, and number of chromosomes is (b) Metaphase.

Step 1: Understand the stages

The first step is to understand what will be the changes in the genetic material during each stage. During interphase, the cell is preparing for division, but the chromosomes are not visible. During prophase, the chromosomes condense and can be seen, but they are not distinctly separate. During metaphase, the chromosomes align in the middle of the cell, and each is distinctly separate from the others making it possible to observe their size, shape, and number. During telophase, the chromosomes start to decondense and become less visible.

Step 2: Finding the best stage

Observing the description of each stage, it's clear that during metaphase, the chromosomes are most visible and are separated from each other. This makes the metaphase the ideal stage to observe the shape, size and number of chromosomes.

Key Concepts

Chromosome Observation

Observing chromosomes involves looking at the structures that carry genetic information in a cell. Chromosomes are visible only during certain stages of cell division. During these stages, they change from a loosely packed form, where they are not visible, to tightly packed structures. These are visible under a microscope.

When observing chromosomes, scientists look for several aspects:

• Shape - Chromosomes have a distinct structure often described as "X-shaped" during certain stages.
• Size - Each chromosome can vary in length, which can be observed and measured.
• Number - Different organisms have different numbers of chromosomes, which is crucial for identifying species.

Making these observations is essential for genetic research and diagnosing genetic disorders. Understanding where and how to look for these features in the cell cycle is key to successful chromosome observation.

Metaphase Stage

The metaphase stage is a critical part of the cell division process known as mitosis. During metaphase, several important changes make it ideal for chromosome observation:

• Chromosomes align at the metaphase plate, a region located in the center of the cell.
• They are attached to spindle fibers, which helps in keeping them taut and easily observable.
• Each chromosome is fully condensed, making their distinct shapes visible.

Metaphase is considered the optimal stage for observing chromosomes because they are lined up neatly. This alignment allows researchers to count and distinguish features such as the centromere position.

The alignment also prepares the chromosomes for separation into the two daughter cells, which is the next stage of mitosis. This separation is essential for ensuring that each new cell receives an exact copy of the genetic material.

Genetic Material Changes

During the cell cycle, genetic material undergoes various changes that are crucial for cell division. Each stage of the cycle contributes differently to the transformation of this genetic material:

• Interphase: This phase prepares the cell for division. The DNA is duplicated, but chromosomes are not yet visible.
• Prophase: Chromosomes condense, becoming shorter and thicker, but they are still not fully aligned or separated.
• Metaphase: Chromosomes align at the center, making them prominent and easy to observe for studies on genetic material.
• Telophase: Chromosomes begin to decondense, returning to their less visible form as the cell completes division.

These changes in genetic material ensure that each daughter cell receives the correct amount and type of genetic material. Understanding these changes is crucial for grasping how cells grow, divide, and how errors in these processes might lead to diseases.