DNA to Chromosome

We always talk about acquiring things genetically, our height, facial features, or even specific eye colours. All these things are complimented to our genes and the elements responsible for these features trail from the Deoxyribonucleic acid (DNA) to the chromosome. 

The cell’s nuclear DNA condenses into accessible chromosomes during mitosis, and the mitotic spindle, a specialised structure composed of microtubules, pulls them apart. 

What are DNA and chromosomes?

DNA is the molecule that carries our genes, or in other words, the part of us that houses all genetic material/information in living organisms. These DNA molecules carry this information in double strands and are therefore shaped as double helixes. Each strand or the stem has a back strand made of deoxyribose (sugar) and other phosphate groups. On the inside, the DNA is further packaged into thread-like streams called chromosomes. 

Chromosomes cannot be observed in the cell’s nucleus, not under even a microscope. During division, the DNA that makes the chromosomes becomes tightly enclosed/packed, and it is then that these chromosomes are visible under a microscope. 

DNA and chromosomes are made of essential components comprising each live organism’s operating system. The cells divide while watching other operations of diverse cell divisions. When a cell splits, the daughter cell inherits some of the parent cell’s functions. Then, the chromatin coils coil into each other to form a complete chromosome. 

Concept of chromosomes

The tightly coiled up DNA forms chromosomes supported and surrounded by proteins called histones. The word chromosome is derived from two Greek words: chroma meaning colour, and soma meaning body. Chromosomes exist in pairs. Human beings carry 23 pairs of chromosomes, making a total of 46 individual ones. Out of these, half are from the biological mother and the other half from the biological father. X and Y chromosomes help in determining the biological sex of humans. Therefore, they are called sex chromosomes. The left-over chromosomes are known as autosomal chromosomes. 

There are two X chromosomes in females, whereas males have one X and one Y chromosome. So, the mother provides an X chromosome to the child, and the father provides either an X or a Y chromosome. The chromosome from the father is responsible for determining the sex of the child.

TYPES OF CHROMOSOMES

There are four types of chromosomes based on the position of the centromere. They are telocentric, acrocentric, submetacentric, and metacentric.

In telocentric chromosomes, the centromere is in the middle and at anaphase. The chromosome forms a V-shape and the two arms are of equal length.

In acrocentric chromosomes, one large and one small arm is formed due to the positioning of the centromere to its end. The chromosome is J-shaped and is in the anaphasic stage.

In submetacentric chromosomes, the two arms are unequal and in the anaphasic stage. The centromere is placed in the subcentral region.

In telocentric chromosomes, the chromosome is placed in the terminal position.

The human genome contains 23 pairs of chromosomes. There are 22 pairs of autosomes and 1 pair of allosomes. 

Autosomes are somatic chromosomes and allosomes are sex chromosomes. 

Function of genes

The chromosomes contain genes that comprise the genetic material that is inherited from one generation to another.

They control the making of structural proteins in the cells and support crucial processes such as cell growth and cell division as well as cellular differentiation.

They have the capacity to replicate and produce exact copies of themselves. These are then passed down to the next generation.

Game of genes

Whether it is the growth rate of the plants or the face structure of children, genes are involved at each stage. Genes are the physical and functional units that are made up of DNA. The primary function of a gene is to provide instructions for forming molecules called proteins. Genes do vary in size from hundred DNA bases to more than two million bases. According to the report from the Human Genome Project, it is stated that humans have around 20,000 to 25,000 genes. People have the same maximum genes, but there are slight variations in a small number of genes, which is the reason behind distinct characteristics between humans. All humans carry two copies of each gene inherited from both parents. Therefore, genes are present in DNA and chromosomes. 

Matter of mutations 

The permanent change in the DNA sequence due to medical issues/conditions is called a mutation. Random changes are mutations that are expected to be deleterious, but some are very beneficial. Mutations are the reasons that support genetic variations and are the source of raw material for human evolution.

There are several types of genetic mutations. Some of which can be classified as:

• Germline mutations: they take place in gametes
• Somatic mutations: take place in other cells in the body
• Chromosomal alterations: they change the chromosomal structure
• Point mutations: they change a single nucleotide
• Frameshift mutations: causes a shift in the reading frame because of reduction or addition of nucleotides

Results of mutations can vary to include:

• The problem in DNA copying during cell division
• Exposure to chemicals called mutagens
• Infection by viruses
• Exposure to radiations such as ionising radiation

Conclusion

Human life is full of changes and is undergoing constant evolution. A Deoxyribonucleic acid (DNA) molecule is arranged in the form of thread-like structures known as chromosomes. Essentially, tightly coiled up DNA forms chromosomes supported and surrounded by proteins called histones. In our body, every cell has 23 pairs of chromosomes, i.e. a total of 46 individual chromosomes. Genes are made up of DNA. they are the smallest functional and physical unit of our body, and they provide instructions to form proteins. The changes in DNA are called mutations, responsible for many diseases and abnormalities. Human beings have around 20,000 to 25,000 genes.