Relationships Between DNA, Genes, And Chromosomes
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The main relationship between DNA, genes, and chromosomes is that genes are made up of segments of coiled DNA, and chromosomes are long supercoiled chains composed of various genes. In humans, a single gene can contain about 1 million base pairs of DNA and a chromosome can contain about 1,000 such genes, and a single cell has 46 of such chromosomes.
DNA, Genes, and Chromosomes are the three important concepts that are needed in understanding the principles of genetics along with inheritance and variation.
These help us understand the evolutionary relations with any living organisms, understand the flow of genetic traits, molecular biology of life, etc.
Earlier it was throughout that proteins were responsible for controlling the genetic traits of any living organism.
But now, with the advancement in molecular biological studies DNA, Genes, and Chromosomes are known to be the controllers of genetic information in any biological body.
These three: DNA, Genes, and Chromosomes are closely related to each other and show its working in a common way in the biological systems in a variety of aspects.
Let’s understand their relationship with each other... But friends, before going to read this article please go through the definitions of Genes, DNA, and Chromosomes provided below to understand each one properly.
Very Important: The Concept of DNA
A DNA molecule is referred to the whole long DNA strand that coils and supercoils itself to take the shape of a chromosome.
The monomer units of DNA are the single nucleotides, and the polymer units are polynucleotides (more than one nucleotides).
A DNA molecule is a polymer of millions of nucleotides attached together one after another in a long chain to form genes, then wraps around the nucleosomes, then forms the chromatin, then the chromatid, and at last forms the chromosomes.
Each nucleotide of a DNA molecule consists of a 5-carbon sugar (deoxyribose pentose sugar), a nitrogen-containing base attached to the sugar, and a phosphate group.
There are four different types of nucleotides found in DNA, differing only in the nitrogenous base. These are Adenine, Guanine, Cytosine, and Thymine.
The four nucleotides are given one letter abbreviations (A/G/C/T) as shorthand for the four bases.
(Image: Thomas Splettstoesser (www.scistyle.com) / CC BY-SA)
What is a DNA?
DNA stands for Deoxyribonucleic Acid is the chemical basis of heredity and may be regarded as the storehouse genetic information at the smallest level possible.
It is the smallest unit that is carrying the genetic information in a living body.
DNA is exclusively responsible for maintaining the identity of different species of organisms from a chemical level over millions of years. Further, every aspect of cellular function is under the direct control of DNA.
The DNA is the smallest chemical basis of genetic information in a living body. A long DNA polynucleotide chain gets organized into genes, the fundamental unit of genetic information.
The DNA in a gene can self-replicate, transcript to mRNA, and from mRNA can translate to proteins.
In a gene, DNA replication, transcription, and translation can occur a lot and so many proteins are produced at the same time. And so all of the proteins that are formed from the various section of the long DNA chain bring out the genetic traits in a living body.
The DNA Double Helix Structure has two strands connected to one another in a twisted ladder form.
Each strand is made up of a polynucleotide chain consisting of a Deoxyribose Pentose Sugar attached to Phosphate group with Nitrogenous bases (Adenine, Guanine, Cytosine, Thymine) being projected from each strand.
What is a Gene?
A gene is a part of a long polynucleotide sequence of the DNA that codes for various proteins that can express a particular genetic trait in the living body.
A gene is basically the physical and functional unit of heredity that stores a particular genetic trait.
Genes can vary in size from having the DNA polynucleotide chain with a few hundred DNA bases to more than 2 million bases.
Genes are part of the chromosomes, which are present in the cell nucleus. A single chromosome can contain hundreds to thousands of genes. Genes are the controller of the inheritance of genetic traits.
Alleles are forms of the same gene with small differences in their sequence of DNA bases and controls the variation in a living body. These small differences contribute to each person’s unique physical features. Just like the gene for height can have the allele of being tall or short if expressed.
In sexually reproducing organisms, everyone has two copies of each gene, one inherited from each parent. During the formation of gametes, one copy of each gene gets passed to one gamete and this leads to the formation of diploid organisms.
In asexually reproducing organisms, the genes are just multiplied and copied to offspring during the reproduction time. This lead to the production of identical offsprings.
In humans, there are about 20,000 and 25,000 genes present in the 23 pairs of chromosomes altogether.
In the case of yeast, there are a total of 6,275 genes on 16 chromosomes that consists of 12 million base pairs of DNA chain.
For example, there are several different alleles for eye color genes, such as blue alleles (blue eyes) and brown alleles (brown eyes).
What is a Chromosome?
In the nucleus of each cell, the DNA molecule is the chemical unit of inheritance, and a long polymer of DNA forms a gene, and when many of such genes get packaged (supercoiled/coiled) into a bigger thread-like structure forms a chromosome.
Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
DNA is so compressible that a DNA helix with a diameter of 2nm (2 x 10-9 m) can be supercoiled to become a chromatid of 700nm (700 x 10-9 m) diameter or so. A chromosome consists of two chromatids attached together.
Chromosomes contain various genes that carry various genetic information as a whole.
The genes on each chromosome are arranged in a particular sequence, and each gene has a particular location on the chromosome called its locus.
In each human diploid cell, there are 23 pairs (46 nos.) chromosomes. One such human Y chromosome contains over 200 genes, at least 72 of which code for proteins. These 200 genes can have about 58 million base pairs of DNA.
Relationships Between DNA, Genes, And Chromosomes
1. DNA is the chemical unit of genetic inheritance which is the part of genes and many of such genes together constitute the structure of a chromosome.
2. A single DNA is a Double Helix Structure of two nucleotide strands. A polymer of many nucleotides forms a gene. Various such genes form a chromosome.
3. DNA contains the chemical structure to code for a few proteins. Genes contain a long polymer of DNA to code for a lot of multiple proteins. And, a chromosome contains various genes that code for a multiple of multiples of proteins.
4. A single DNA nucleotide cannot express a genetic trait. A gene with a huge polynucleotide of DNA can express a specific genetic trait. And, a chromosome that contains a lot of genes can express various genetic traits as a whole.
5. DNA has the ability to coil and supercoil. It’s a way of the packaging itself to fit inside the nucleus of the cell. And in doing so, DNA makes genes and genes subsequently make chromosomes.
6. DNA is the chemical unit of hereditary, Gene is the functional unit of hereditary, and Chromosome as a whole is the carrier of hereditary information from generation to generation.
7. DNA Topoisomerases are universal enzymes found in all cell types. These enzymes act on DNA Helix to coil it to make a gene which further coils to make a nucleosome. Various nucleosomes coil further using that same enzyme to form a Chromosome. That’s how DNA is coiled and supercoiled to form a chromosome.
8. Chromosomes are the carrier of both genes and DNA because it contains both. In reality, the chromosome is not other than the supercoiled structure of DNA itself.
9. DNA takes part in replication and transcription for a particular gene and also for the overall chromosome to form various proteins. It’s only the DNA in the genes and chromosomes that take part in replication and transcription and thus forming proteins.
10. Genes are those chunks of DNA that contains the information of how, when, and why to code for proteins. It has the information to stop or start DNA replication, transcription, and further the translation process.
11. Genes are the chunks of DNA that pass from the parents to offspring. Genes are just like the processor and motherboard of the genetic information.
12. The activity of the whole chromosome is controlled by the various genes present in it. And, the gens are directly dependent on the structure of the DNA present in it.
13. Each DNA nucleotide is independent of each other, but the DNA polynucleotide can work together as a unit when present in a particular gene thus able to express a particular genetic trait.