Mutation




Before you go for a  discussion about mutation you must have some idea about the terms variation and recombination. All living organisms, from the tiniest bacteria to plants and human beings are built up from microscopic cells. Mutations are changes that occur in the nucleotide sequence of DNA.

Variation

Variation may be defined as the process whereby closely related organisms come to differ amongst themselves. Variations are of highest significance in organic evolution as without variation no change could occur. That may be small, slow and continuous, but sometimes an impulsive change in genetic constitution leads to large variation.

Recombinations

The organisms which express characters of both the parents are known as recombinants and the occurrence responsible for mixing material and parental characters in sexually reproducing organisms is said to be recombination. Genetic variation in sexually reproducing species arises primarily because parental genes are shuffled into new combinations that are new genotypes in the offspring. Now we shall go for the subject of mutation.




What is Mutation?

Mutations in a wide sense include all those inherited changes which alter the phenotype of an individual. While working on evening primrose, scientist Hugo de Vries (1901) used the term mutation to describe phenotypic changes which were heritable. The term 'mutation' was first introduced by him when he observed the sudden variations in the plant, evening primrose and this sudden variation was called mutation by him.

Mutation can be defined as an event that gives rise to a ht alteration in the structure of a gene or chromosome or a change in chromes, number. The organism in which mutation occurs is known as a mutant.
Mutations may occur spontaneously in nature or they may be artificially induced- Spontaneous gentle mutations are always occurring in nature. In about 10 million specimens of Drosophila melanogaster, a few hundred gene mutants were observed. These mutants produce true-breeding stable genotypes varying in characters like eye colour, wing type, etc. from the original wild type. The artificially induced mutations are similar to those produced spontaneously in nature due to the fact that the kinds of changes produced are alike to those created by spontaneous mutations.

What is Spontaneous mutation?

The Spontaneous mutations originate spontaneously in nature. They continuously arise in nature automatically.
They are produced by naturally occurring mutagenic agents such as electric currents, atomic particles and rays, temperature, variations, etc. and their frequency of occurrence is very low.




What is induced mutation?

The induced mutations are induced artificially. They are man-made and, therefore, occur when man induces them, otherwise never found. They are produced by subjecting organism artificially to mutagens such as gamma rays, X-rays, neutrons, ultraviolet rays, etc. Their frequency of occurrence is comparatively higher than Spontaneous mutation.

At where is the mutation found?

Mutations are observed in all organisms from man to bacteria. They arise all on a sudden. Most mutations bring about such minute changes that escape common observation. Mutations may be dominant or recessive, sex-linked or autosomal, germinal or somatic, lethal or non-lethal, and useful or deleterious. But most mutations are recessive and lethal, possibly because they disturb genie balance. They produce their effect only in a homozygous form in some future generation.



Types of mutation

Mutation is a heritable change in the structure of a gene or chromosome, or a change in chromosome number. Accordingly, mutations are of the three principal types, those are:
i) Gene mutations
ii) Chromosomal mutations
iii) Genomatic mutations or polyploidy.

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