Biological Chromosomes | Anthropology Optional for UPSC PDF Download

Introduction

Chromosomes are thread-like structures located within the nucleus of both plant and animal cells. They are crucial as they carry the fundamental genetic material known as DNA. Chromosomes were initially discovered by Strasburger in 1815, and the term "chromosome" was first coined by Waldeyer in 1888. In humans, there are 46 chromosomes, organized into 23 pairs. In the following discussion, we will delve deeper into the structure of chromosomes and their significance.

Definition of Chromosome

“A chromosome is a thread-like structure composed of proteins and found within the nucleus of all cells. It carries the fundamental genetic material, known as DNA, which is responsible for transmitting genetic information from one generation to the next.”.

Structure 

A chromosome is generally composed of eight parts, including the centromere, chromatids, chromatin, secondary constriction, telomere, chromomere, chromonema, and matrix.

• Centromere or Kinetochore: This is the central region of the chromosome where spindle fibers attach during cell division. The centromere plays a crucial role in the movement of chromosomes during the anaphase stage of cell division.
• Chromatid: During cell division, each chromosome is divided into two identical halves connected by a centromere. Each half is known as a chromatid, and they both contain DNA. The chromatids separate during the anaphase stage of cell division to form independent chromosomes.
• Chromatin: Chromatin is a complex mixture of DNA and proteins that form chromosomes within the nucleus of eukaryotic cells. To fit within the nucleus, nuclear DNA is tightly condensed and wrapped around proteins. Chromatin is composed of DNA, RNA, and protein.
• Secondary Constriction: This region is typically involved in organizing the nucleolus, a structure within the nucleus.
• Telomere: The telomere is the end region of each side of the chromosome. Each chromosome has two telomeres, which help protect the chromosome from damage.
• Chromonema: This is a coiled, thread-like filamentous structure with chromomeres arranged along its length. The chromonema helps maintain the chromosome's size and serves as a site for gene-bearing.
• Chromomeres: These bead-like structures are located on the chromonema and are arranged in a row along its length. Each chromosome has a constant number of chromomeres, which are responsible for carrying genes during cell division to the next generation.
• Matrix: The matrix is a jelly-like substance found inside the pellicle, a membrane that surrounds each chromosome. The matrix is composed of non-genetic materials.

Functions of Chromosomes

In 1902, Sutton and Bover first proposed the idea that chromosomes play a significant role in heredity.

• Chromosomes serve as the carriers of essential genetic material, specifically DNA, which contains the necessary genetic information for various cellular functions. These functions are crucial for the growth, survival, and reproduction of living organisms.
• Chromosomes are covered by histones and other proteins that act as a protective layer against chemical and physical forces, such as enzymes. This protective function is particularly important during cell division, as it helps prevent damage to the genetic material within the DNA.
• During the process of cell division, spindle fibers attach to the centromeres of chromosomes and contract. This contraction ensures an accurate distribution of genetic material, or DNA, to the newly formed daughter nuclei.
• In addition to histones, chromosomes also contain non-histone proteins. These proteins play a role in regulating gene activity. Gene-regulating cellular molecules function by activating or deactivating these proteins, which in turn causes the chromosome to expand or contract. This process enables the precise control of gene expression, allowing cells to function efficiently and correctly.

Examples of Types of Chromosomes

• Metacentric Chromosomes: In metacentric chromosomes, the centromere is located precisely in the middle of the chromosome, resulting in two equal-length sections. For example, human chromosomes 1 and 3 are metacentric.
• Submetacentric Chromosomes: Submetacentric chromosomes have a centromere that is not exactly in the center. Instead, it is slightly off-center, leading to asymmetrical sections of different lengths. Human chromosomes 4 through 12 are examples of submetacentric chromosomes.
• Acrocentric Chromosomes: In acrocentric chromosomes, the centromere is significantly offset from the center, causing one strand to be much longer than the other. Human chromosomes 13, 15, 21, and 22 are acrocentric.
• Telocentric Chromosomes: Telocentric chromosomes have a centromere located at the very end of the chromosome. While some species, such as mice, possess telocentric chromosomes, humans do not have any telocentric chromosomes.

Conclusion

Chromosomes are essential thread-like structures found within the nucleus of all cells, carrying the vital genetic material known as DNA. They play a crucial role in heredity, gene regulation, and protecting genetic material during cell division. Chromosomes are composed of various parts, including the centromere, chromatids, chromatin, and telomeres, each with specific functions. There are different types of chromosomes based on the location of the centromere, such as metacentric, submetacentric, acrocentric, and telocentric chromosomes. Understanding the structure and function of chromosomes is fundamental to comprehending the processes of inheritance, gene expression, and cellular function in living organisms.

Frequently Asked Questions (FAQs) for Biological Chromosomes

What are chromosomes made of, and where are they found?

Chromosomes are made of proteins and DNA, which carry the genetic information necessary for various cellular functions. Chromosomes are found within the nucleus of all plant and animal cells.

What is the primary function of chromosomes in living organisms?

The primary function of chromosomes is to serve as carriers of essential genetic material, specifically DNA. This genetic material contains the necessary information for various cellular functions, such as growth, survival, and reproduction, making chromosomes crucial in the processes of inheritance and gene expression.

What is the difference between metacentric, submetacentric, acrocentric, and telocentric chromosomes?

The difference between these types of chromosomes lies in the location of the centromere. In metacentric chromosomes, the centromere is in the middle, resulting in two equal-length sections. In submetacentric chromosomes, the centromere is slightly off-center, leading to asymmetrical sections. In acrocentric chromosomes, the centromere is significantly offset, causing one section to be much longer than the other. In telocentric chromosomes, the centromere is located at the very end of the chromosome.

How do chromosomes protect genetic material during cell division?

Chromosomes are covered by histones and other proteins that act as a protective layer against chemical and physical forces, such as enzymes. This protective function is particularly important during cell division, as it helps prevent damage to the genetic material within the DNA. Additionally, spindle fibers attach to the centromeres of chromosomes during cell division, ensuring an accurate distribution of genetic material to the newly formed daughter nuclei.