Variation in the individuals either induced by environment or due to the hereditary change during genetic recombinations. But the variations or changes which suddenly appear in an individual and can be inherited to the progeny, is called mutation (Dwain).
According tobateson: Mutation is discontinuous variation.
According to sinnot DON, Dobznhansky, Mutation is any change in gene or genotype.
According to hugodevries mutation is defined as any sudden and drastic heritable change in gene which is not traceable or ascribable to segregation or recombination. He first recognised the sudden changes in Oenothera Lamarkiana and studied the hereditary and came to this condition in 1901.
Mutations may be induced or natural it is brought about by any change in the genetic makeup either in chromosome level or in gene level. It may be structural or compositional or numerical changes which cause the change in character of an individual. A character may be lost or gained.
Mutation play important role in plant breeding and also displays the key role in evolution of species.
Role of Mutation in Plant Breeding:
Plant breeding aims at improving the crop quality but improving the heredity through the cross hybridization technique. In plants mutations can be artificially incused by mutagenic agents and there utilization for production of new superior varieties of species from traditional variety. This process is called mutation breeding.
The history of mutation breeding in India started in 1935 at Bose research institute, Calcutta and established at IARI, New Delhi in 1959.
a) Mutation breeding in wheat (Triticum species):
By the application of Eradication and chemical mutagens mutation being used to introduced in wheat varieties. By this process the resistance variety NP836 was derived from NP 799 at India agricultural research institute (IARI), New Delhi. This is done by application gamma ray on NP 799 variety of wheat. Thus NP 836 is a mutant variety.
b) Mutation breeding in rice (Oryzaesativa):
Mutation breeding in rice is very common in south and south-east Asia. In rice certain chemical mutafgenens has been used to produce polyploid varieties of rice and hybridised with the diploids producing high yielding and resistant varieties.
The high yielding varieties of rice produced by mutation breeding is P 500.28. This variety is obtained from the T-1145 variety at Bose’s institute, Calcutta.
c) Mutation breeding in cotton (Gossypium):
Mutation beading achieved evolving improved variety in cotton. A caiety named indore-2 was developed from “Malwa Upland -4” by X-ray treatment.
Mutations in thevariey mescilla cabala by X-ray treatment result increase in 40-50% in fibre production.
M.A.2 H-190. Indore-2 L.SS Bury-0394, 320-F and H-14 are mutation improved varieties of cotton.
d) Mutation breeding in sugarcane:
Both eradication and chemical mutagens are used to induce maturation in sugarcane. In sugarcane nodal buds are exposed to radiation in field and the mutant buds or tillers are selected in F1 and F2 generations through artificial crosses.
Some popular higher quality sugarcane varieties evolved through mutation breedng are H.M.658, H.M. -661, Co-213, Co-602, Co-612 etc.
e) Mutation breeding in potato:
Mutations also introduce in potato crop through mutation breeding. It aims at the production of early harvesting varieties and high yielding variety.
These includes eradication and chemical mutagenic products and through cross breeding. This is done in flowering or by exposing the seed tubers.
(II) Role of Mutation in Evolution:
Mutation play a key role in evolution and origin of new species. According to the mutation theory as propounded by Hyge de Vries (1901), a new species arise not by gradual accumulation of small variations, but by the appearance of permanent and sudden change in character which is unpredictable. He explained the process as the mutation.
While working on the plant named Oenothera Lamarkiana de Vries marked sudden heritable changes and put forwarded that:
a) New species arises due to mutations.
b) Mutation brings the chances of selection.
c) Mutation takes place nearly at all directive and may involve any character.
In Oenothera chromosome number is 14 but de Vries observed that in some generations this chromosome number tend to vary and in some it was found 15, 16, 20, 22, 24, 27 ,28, 29 and 30. This results in variation of flower size shape arrangement of buds and size of seeds etc.
Stebbins (1971) has proposed some basic process of evolution as in terms of neo Darwinism and pointed out that evolution is brought about by gene mutations or chromosomal mutation.
According to Stebbins:
i) Mutation is gene level cause alterations in the structure and position of gene on chromosome called point mutation.
ii) This results in the alteration of phenotype of an organism.
iii) Changes in basic chromosome number either any addition of loss of any set or parts of them cause appearance of disappearance of new characters.
iv) Once the mutation in gene level or chromosomal level is firmly established in populations, they are subjected to natural selection.
Natural selection is the key process of organic evolution.