Problem 159 - Objective Biology for NEET

Question

Based on the position of centromere, the chromosomes are classified into how many types? (a) 1 (b) 3 (c) 2 (d) 4

Step-by-Step Solution

Answer

The chromosomes are classified into 4 types based on the position of the centromere.

Step 1: Understand the information provided

In this question, we are asked to find out how many types chromosomes are classified into based on the position of the centromere. The centromere is the part of a chromosome that links sister chromatids (or a pair of chromosomes). It is essential for the segregation of chromosomes during the process of cell division.

Step 2: Apply the knowledge about chromosomes

Chromosomes are grouped in several ways, one of which is based on the location of the centromere. Specifically, chromosomes can be categorized into four types depending on the location of the centromere. These four types are: metacentric, submetacentric, acrocentric, and telocentric.

Step 3: Match the information with the provided options

Looking at the options provided (1, 3, 2, and 4), the correct answer would be 4 because chromosomes are divided into four types depending on the position of the centromere.

Key Concepts

Centromere

The centromere is a crucial part of a chromosome with a specialized structure that plays a pivotal role in cell division. Its primary function is to ensure the proper distribution of duplicated chromosomes, called sister chromatids, between two daughter cells during both types of cell division – mitosis and meiosis. The position of the centromere gives chromosomes a distinct shape and can be used to classify them into different types.

For example, during the metaphase stage of cell division, chromosomes line up in the center of the cell, with the centromere being the exact region where spindle fibers attach to pull the chromatids apart. This process is fundamental for genetic stability, as any errors in chromosomal segregation could lead to genetic disorders or cell death. Understanding the characteristics of the centromere, including its location and function, is important for disciplines such as genetics, cytogenetics, and molecular biology.

Types of Chromosomes

Chromosomes are thread-like structures present in the nucleus of cells, composed of DNA and proteins. They carry genetic information that determines the traits of an organism. When it comes to classification based on the centromere location, there are four major types of chromosomes:

• Metacentric: These have a centrally located centromere, giving the chromosome two arms of equal length.
• Submetacentric: These chromosomes feature a centromere that is offset from the center, leading to one shorter arm and one longer arm.
• Acrocentric: In these chromosomes, the centromere is situated close to one end, resulting in a very short arm and a very long arm.
• Telocentric: These have a centromere at the extreme end, effectively having one arm.

The knowledge of these types is not merely academic; it has practical implications in areas such as karyotyping, which is used to diagnose genetic diseases and anomalies in chromosome number or structure.

Chromosomal Segregation

Chromosomal segregation refers to the equally precise separation of sister chromatids into two new daughter cells during cell division. This process ensures that each daughter cell receives the correct number of chromosomes, maintaining the species-specific chromosome number. The process is tightly controlled and involves several steps, starting with the replication of the chromosomes during the S phase of the cell cycle and ending with their separation in the anaphase of cell division.

Errors in chromosomal segregation can lead to conditions called aneuploidies, where cells have an abnormal number of chromosomes, such as Down syndrome, which is caused by an extra copy of chromosome 21. Therefore, understanding the mechanisms of segregation, including the role of the centromere and spindle fibers, can help us appreciate the complexity of genetic inheritance and the origins of chromosomal disorders.