Genetic variation among individuals provides the raw material for the ultimate source of evolutionary changes. Mutation and recombination are the two major processes responsible for genetic variation. A sudden change in the genetic material of an organisms is called mutation.
The term mutation was introduced by Hugo de Vries (1901) while he has studying on the plant, evening primrose (Oenothera lamarkiana) and proposed ‘Mutation theory’. There are two broad types of changes in genetic material. They are point mutation and chromosomal mutations. Mutational events that take place within individual genes are called gene mutations or point mutation, whereas the changes occur in structure and number of chromosomes is called chromosomal mutation. Agents which are responsible for mutation are called mutagens, that increase the rate of mutation. Mutations can occur either spontaneously or induced. The production of mutants through exposure of mutagens is called mutagenesis, and the organism is said to be mutagenized.
Types of mutation
Let us see the two general classes of gene mutation:
•Mutations affecting single base or base pair of DNA are called point mutation
•Mutations altering the number of copies of a small repeated nucleotide sequence within a gene
Point mutationIt refers to alterations of single base pairs of DNA or of a small number of adjacent base pairsTypes of point mutationsPoint mutation in DNA are categorised into two main types. They are base pair substitutions and base pair insertions or deletions. Base substitutions are mutations in which there is a change in the DNA such that one base pair is replaced by another . It can be divided into two subtypes: transitions and transversions. Addition or deletion mutations are actually additions or deletions of nucleotide pairs and also called base pair addition or deletions. Collectively, they are termed indel mutations (for insertion-deletion).Substitution mutations or indel mutations affect translation. Based on these different types of mutations are given below.
The mutation that changes one codon for an amino acid into another codon for that same amino acid are called Synonymous or silent mutations. The mutation where the codon for one amino acid is changed into a codon for another amino acid is called Missense or non-synonymous mutations.
The mutations where codon for one amino acid is changed into a termination or stop codon is called Nonsense mutation. Mutations that result in the addition or deletion of a single base pair of DNA that changes the reading frame for the translation process as a result of which there is complete loss of normal protein structure and function are called Frameshift mutations.