According to Hugo Dear Sirs, Vries (1884-1935) mutation is defined as any sudden and drastic change in gene which can be heritable but is not traceable or ascribable to segregation or recombination. He first recognized the sudden changes in Oenothera Lamarkiana (changes in colour and shape of flower) and studies the hereditary process and came to this conclusion in 1901.
Mutation may be included or Natural, it is brought about by any change in the genetic make up, either at Chromosome level or at gene level. This change may be structural, or compositional or numerical which leads to the change of characters all of sudden in an individual life time. It can be transferred from the progeny to the next generation. This change may involve loss or gain or modification of a character or characters.
(I) Chromosomal Mutation:-
Chromosomal Mutation are the changes in chromosomal architecture. This may be due to change in gross morphology of chromosomes or changes in the number of chromosomes(Polyploidy).
a) Chromosomal Aberrations:-
This is the structural or morphological rearrangement in chromosome which takes place during pachetene stages of meiosis. There are following types.
i) Deficiency and delation.
Due to above changes location of gene or part of chromosome is dislocated, lost or may be new segment is added which bring about sudden changes in characters.
b) Polyploidy: –
Due to defective cell division in somatic cells or due to fusion of diploid gametes set of individual changes. It may be multiple of true genomic set or addition of some extra genome. This is found in plants. Ploidy changes from normal diploid (2n) to 3n, 4n, 6n, 8n etc. or 2n+1 or 2n+2 or 2n+1 etc.
II) Genomatic Mutation:-
This is the change in the molecular arrangement of DNA which bring about by defectives base pairing. In this case tautomeric form of a base unusually pairs with another alternate base. Suppose Adenine normally pairs with Thymine. But tautomeric Adenine can pairs with normal cytosine and so on This results in the unusual change in base sequence leading to change in characters.
Mutation play an important role in evolution of new species. It may artificially induced for crop improvement in producing mutation crops by application of mutagenic agents like Mustardgas, urethane. formaldehyde etc.