Mutations

Mutations - Mutation is defined as the sudden heritable change in the genetic material of an organism. The term mutation is applicable to both the change in genetic material and to the process by which the change occurs. Thus the term mutation is used to define the process as well as the effect.

Mutation is simply an alteration in the nucleotide sequence of a DNA molecule. Physical agents like UV or chemical molecules like Et.Br can cause mutations. Molecules or agents that cause mutations are called as mutagens. Mutations occur randomly or non specifically and there is no defined process or machinery to carry out mutation in a cell or organism.

Recombination on the other hand occurs at a particular time, with the help of a set of enzymes (e.g. Rec) and in a defined process. Thus mutation and recombination are not the same. But mutation and recombination are central events in genetics and evolution.

The process by which the rate of mutation is increased either by using physical or chemical agents is called as mutagenesis. Mutations created in an individual by the process of mutagenesis are called as induced mutations.

Those mutations that occur without any cause are called as spontaneous mutations. Spontaneous mutations are regarded as accidental, unintended, unidirectional, unoriented random events. Even today we have no way to tell where or when a mutation will occur in a cell, cell organelle or gene. Spontaneous mutations are deviations from a natural process.

Literally speaking, it is not possible to prove that a particular mutation is a spontaneous mutation or an induced mutation. But for the sake of convenience, mutations are classified into various groups and subgroups. Mutations can be looked at from three different angles.

1. DNA mutations
2. Chromosomal mutations
3. Organism or phenotypic mutations
All mutations take place in the gene, DNA sequence or nucleotide, but depending upon the site where their effect is visualized, they are classified into the types mentioned above.