What Are Chromosomes And Its Functions? CBSE Class 12 Biology Notes

Biology offers the door to many professional options, including medicine and other fields. Students can achieve full marks in the CBSE Class 12 Biology Board Exam with adequate study because it is primarily a theoretical subject. However, a well-planned study schedule, effective CBSE Class Biology preparatory advice, and information on all important topics. “Chromosomes” is an important CBSE Class 12 Biology topic. The definition, structure, and functions of chromosomes are highlighted in the article. These notes would benefit students studying for the CBSE Class 12 Biology Board Exams in 2022. Students must use NCERT Solutions for Class 12 Biology for a better understanding of the topic!

CBSE Class 12 Biology: Chromosomes

Chromosomes can be defined as thread-like structures present in the nucleus of the eukaryotic cells that contain tightly packed DNA. These are found in the nucleus of both plant and animal cells. It can alternatively be defined as a DNA molecule containing some or all of an organism’s genetic material. DNA is coiled around proteins known as histones, which provide structural support. Chromosomes play a vital role in ensuring that DNA is duplicated and distributed correctly during biological processes.

The primary role of chromosomes is to transport the basic genetic information known as DNA, which is required for the cells’ growth, development, survival, and reproduction activities. 

The thread-like structure present in the chromosome is known as chromatin fibre. It is structured so that it resembles a spool of yarn. The chromatin fibre comprises histone protein molecules coiled in a string-like structure. These strings contain a chain of DNA made up of millions of long nucleotides consisting of hundreds of genes along its length. Use NCERT Solutions for Class 12 Biology to understand the topic of chromosomes effectively. 

CBSE Class 12 Biology: Structure of Chromosomes

A chromosome structure is made up of eight parts:

• Centromere (also known as Main Constriction or Kinetochore)

The centromere, also known as the kinetochore, is the main constriction at the centre of the cell to which the chromatids or spindle fibres are linked. Its function is to allow chromosomal mobility during the anaphase phase of cell division.

• Chromatids 

In cell division, the chromosome is split into two identical half strands connected by a centromere. A chromatid is formed by joining the two halves of a chromosome. Each chromatid contains DNA and separates to form a separate chromosome during Anaphase. The centromere links the two chromatids together.

• Chromatin

It is a complex of DNA comprising DNA, RNA and protein that creates chromosomes inside the nucleus of eukaryotic cells (plants and animal cells). Nuclear DNA is extremely compacted and coiled around nuclear proteins to fit inside the nucleus. In other words, it does not exist in the form of free linear strands. Chromatin is majorly composed of DNA, RNA, and protein.

• Secondary Constriction 

It is commonly found in nucleolar structures.

• Telomere 

A telomere is a terminal region on each half of the chromosome.

• Chromomere

It is a thread-like coiled filament structure that contains chromosomes. Chromonema regulates chromosomal growth and serves as a gene-bearing region.

• Chromonema 

It refers to the bead-like structures found on threads or chromonema. These are lined up all along the length of the chromonema. The number of chromosomes is fixed, and it is responsible for passing on genes to the next generation during cellular division.

• Matrix

A pellicle is a membrane that surrounds each chromosome. The matrix is the jelly-like substance found inside the pellicle. It is made from non-genetic materials.

Also See: CBSE Class 12 Syllabus | CBSE Class 12 Biology Syllabus

CBSE Class 12 Biology: Functions of Chromosomes

The primary function of chromosomes is to transmit the basic genetic material – DNA. DNA contains genetic information, which is necessary for various biological processes. These functions are necessary for organisms’ growth, development, survival, and reproduction. Read the NCERT Solutions for Class 12 Biology  for concept clarity.

Histones and other proteins form a protective layer around the chromosomes. These proteins shield it from chemical and physical stimuli (e.g., enzymes). Thus, chromosomes also safeguard the genetic material (DNA) during the division of cells.

Spindle fibres connected to the centromeres play a key role during cell division. The shrinking of chromosomal centromeres ensures the accurate distribution of DNA (genetic material) to daughter nuclei.

Histone and non-histone proteins are present inside chromosomes. These proteins control gene activity. These proteins are activated or deactivated by cellular substances that regulate genes. This activation and deactivation cause the chromosome to grow or contract.

Conclusion

Cells need to repair constantly to expand and rejuvenate. Cell division is essential for an organism’s growth and development. During cell division, chromosomes guarantee that DNA is distributed evenly among daughter cells. But sometimes, even a minor flaw in the process can result in various diseases and abnormalities. Cancer is caused by uncontrolled cell division, which results in tumour cells. A chromosomal abnormality, such as a change in structure or quantity, can result in genetic abnormalities such as Down syndrome, Turner syndrome, etc. Defective chromosomes can potentially cause severe disease in humans. 

A chromosome is an important topic from the CBSE Class 12 Biology Exam point of view. Studying these notes along with NCERT Solutions for Class 12 Biology will help students gain comprehensive information on the topic, ensuring higher grades in their Biology Exams! 

FAQs

1. What exactly is a chromosome?

Chromosomes can be defined as thread-like structures in the nucleus that contain tightly packed DNA. Alternatively, it can be described as a DNA molecule containing some or all of an organism’s genetic information. DNA is coiled around proteins known as histones, which provide structural support. Chromosomes play a crucial role in ensuring that DNA is duplicated and distributed correctly during biological processes.

Chromosomes exist within the nucleus of animal and plant cells. Each chromosome is composed of protein and one unit of deoxyribonucleic acid (DNA). This genetic information is passed down from parents to children; DNA includes detailed instructions that distinguish each kind of living species.

The name chromosome is derived from the Greek terms for colour (chroma) and body (bodies) (soma). Scientists gave this name to chromosomes by scientists because they are cell structures or entities intensely stained by several coloured dyes employed in the study.

2. What are the functions of chromosomes?

The chromosome’s unusual shape keeps DNA firmly wrapped around spool-like proteins called histones.

Cells must continuously divide to make new cells to replace old, damaged cells for an organism to survive and operate effectively. DNA must remain undamaged and equally distributed throughout cells during cell division. Chromosomes play a significant role in ensuring that DNA is appropriately replicated and transmitted in the process of cell division. Still, there are chances of mistakes happening on rare occasions.

Changes in the number or shape of chromosomes in new cells might cause major issues. For Instance, in humans, damaged chromosomes can cause severe diseases such as leukaemia and other malignancies in the human body.

It is also important for reproductive cells, such as eggs and sperm, to have the correct amount of chromosomes and that those chromosomes are properly structured. If this is not done, the developing embryos may not develop appropriately. For Instance, individuals with Down syndrome have three copies of chromosome 21, rather than the two copies found in normal people.

3. What exactly are centromeres?

The centromere is the restricted region of linear chromosomes. Although this constriction is known as the centromere, it is not always placed in the centre of the chromosome and, in some situations, is near the end of the chromosome. The area on each centromere side is known as the chromosome’s arms.

Centromeres aid in the precise alignment of chromosomes throughout the complex cell division process. The centromere acts as an attachment location for the two halves of each duplicated chromosome, referred to as sister chromatids, as chromosomes are duplicated in preparation for forming a new cell.

4. Do all living beings have the same chromosomal types?

The number and form of chromosomes differ between living beings. A vast majority of bacteria species contain one or two circular chromosomes. Like other plants and animals, humans have linear chromosomes organised in pairs within the cell’s nucleus.

The only human cells that lack chromosome pairs are reproductive cells, or gametes, with only one copy of each chromosome. When two reproductive cells combine, they form a single cell, combining two copies of each chromosome. This cell then divides, and its descendants divide several times more, finally generating a complete individual with a complete set of paired chromosomes in about all of its cells.

Aside from the linear chromosomes present in the nucleus, human and other complicated species’ cells include a much smaller form of chromosome comparable to those found in bacteria. The circular chromosome present in mitochondria helps the organelle function as the cell’s powerhouse. 

5. How are chromosomes passed on from generation to generation?

In complex creatures such as humans, one copy of each chromosome is obtained from the female parent and the other from the male parent in humans and most other co. It explains why children get characteristics from their mother and others from their father.

The tiny circular chromosome found in mitochondria has a unique inheritance pattern. Only egg cells, not sperm cells, retain their mitochondria during fertilisation. As a result, mitochondrial DNA is always passed down from the female parent. A few human illnesses, including various forms of hearing problems and diabetes, have been linked to mitochondrial DNA.

6. What exactly are telomeres?

Telomeres are DNA segments repeated at the ends of linear chromosomes. It ensures the safeguard of the ends of chromosomes.

In most cell division processes, telomeres lose a small amount of DNA. When the entire DNA of the telomere is lost, the cell can no longer replicate and dies.

White blood cells and other cell types that can divide rapidly have a unique enzyme that preserves their chromosomes from losing the DNA present in the telomeres. Because these cells preserve the DNA present in telomeres, such cells live longer than others.

7. How many chromosome pairs are present in human cells?

Humans contain 23 chromosome pairs, making a total of 46 chromosomes.

Each plant and animal cell has a unique set of chromosomes. Taking an example of a fruit fly, it has four pairs of chromosomes, but a rice plant has twelve, and a canine has forty-nine.