Mutation: Sudden and heritable change in any characteristic of an organism is called a mutation. Mutations are spontaneous in nature but are induced in very high frequency by certain factors.
Types of Mutation
On this basis, mutations are divided into the following two categories. Such as:
|Type (s)||Subtype (s)|
|Spontaneous Mutation / Auto mutation||No subtypes|
|Induced Mutation||1. Physical|
1. Spontaneous Mutation
The mutation which occurs spontaneously in nature due to natural causes is given the name of spontaneous mutation.
This may be due to the following:
- error by DNA polymerases during DNA replication
- self-demethylation of DNA bases
- activation of variable components and
- Automatic mutation, occurs by solar radiations and chemical pollutants present in the atmosphere.
2. Induced Mutation
When mutations occur due to foreign activity or on treatment with a physical or chemical factor, they are called induced mutations. The factors which induce mutation are called mutagen.
These are of two types, such as –
- Physical factors – such as-x-rays (x-rays), gamma-rays (Υ-rays), neutrons and ultraviolet rays, etc.
- Chemical factors – Sodium azide, such as hydroxyalanine nitrous acid, ethylmethane sulfonate and nitrogen mustard, etc.
The reason for the origin of both the above types of mutations is actually a change in the ‘gene structure‘ i.e. the base sequence of the respective DNA molecule.
Mutation of Gene Level
Mutations in DNA molecule signaling genes alter the sequences of amino acids in the proteins synthesized under the control of these genes and may affect the appearance of genetic traits.
These mutations at the gene level have the following categories:
1. Silent Genetic Mutations
In this, the code changes due to the change of the third position nucleotide in any triplet code of the gene, but the new code also contains the signal information of the same amino acid of the old code.
Hence, there is no effect of such mutation on the resultant polypeptide chain. For example, the gene code for the CUU codon of an mRNA molecule can be changed to the gene code for the CUA codon, but both contain the signaling information of the amino acid leucine.
2. Missense Mutations
In this, a nucleotide of the first, second or sometimes third position in a triplicate signal of a gene is changed to code for the information of another amino acid.
If the location of this new amino acid in the resulting polypeptide chain is not significant, the metabolic role of the protein is not significantly affected, otherwise, the protein may be defective.
This leads to distortion in the associated visual symptoms. A classic example of this comes from a disease called sickle-cell anemia in humans.
3. Nonsense Mutations
In this, a nucleotide in a triplicate code of a gene is changed such that the original code becomes the code for the termination codon–UGA, UAA or UAG) of the mRNA molecule.
Thus the resulting polypeptide chain remains incomplete and has a significant effect on the associated trait.
4. Frameshift Mutations
In this, one or two or more (not in multiples of three) nucleotide molecules are removed or new nucleotide molecules are added from any locus of the gene.
Hence, from this point onwards the sequence of the triplet signals changes completely. As a result, the resulting protein is of a completely different type and the associated visual character is distorted.
Characteristics of Mutation
From the facts known so far, it is clear that there is no difference in the nature of spontaneous and induced mutations.
Some of the main characteristics of mutations are given below.
- Most of the mutant alleles are recessive.
- Whether a mutation occurs in a particular gene or not depends only on chance.
- Most of the mutations are of deleterious effect. About 0.1 percent of mutations are beneficial.
- Mutations take place spontaneously in nature. The spontaneous mutation rate for a gene can generally range from 10‾8 to 10‾7 (from one in ten thousand to one million).
- The auto mutation rate of different genes is different.
- The induced mutation rate is relatively high when treated with mutations in certain stages of cell division, e.g., S phase (DNA synthesis).
- Most of the induced mutations are poliotropic.
Application of Mutation
- Mutation is used to produce more variation. But keep in mind that mutation is not a substitute for germplasm collections.
- Various quantitative traits including yield can be improved by mutation breeding.
- To improve anyone oligogenic trait of an excellent and adapted variety.
- Undesirable linked genes can be removed by this method.
- The desired genes from wild species can be transferred to crops.
Who is called Mutant?
The member in which the mutated trait appears first is called a mutant.
Who is the father of mutation?
Hugo de Breeze (1900) (UPPCS Main)
Who was the first to cause mutations in the Dromophia fly by X-rays?
H.J. Muller (1927) (UPPCS)
Why did Muller receive the Nobel Prize in 1946?
For Mutation by -x-ray
Who discovered the mutagenic properties of mustard gas and many other chemicals?
Arbach & Robson
One of the reasons that cause new species to arise in nature is?
What is the source of genetic diversity present in an organism?
Mutation and Recombination (IAS)