(Induced Mutations for Crop Improvement)
What is mutation?
Mutation is the “Sudden heritable change in an organism”. Mutation may be the change in gene, chromosome or plasmagene (genetic material inside mitochondria and chloroplasts. The mutation produced by change in the base sequence of gene is called point mutation or gene mutation. The gene mutation may be further classified as transition, transversion, deletion, duplication or inversion. Chromosomal mutations are the change in chromosome structure. The change in the structure of chromosome can occur as a result of large deletion, inversion, duplication, translocation and change in chromosome number. Most of the mutations are lethal to the organism. A very small number of mutations are beneficial to the organism. Additionally, by the use of mutation inducing agents, a breeder can induce desirable changes in the genetic constitution of plants and thereby he can improve the performance of a cultivated variety.
Definition: “The utilization of induced mutations in crop improvement is called mutation breeding”
The term mutation breeding was first coined by Freisleben and Lein in 1944 to refer to the deliberate induction and development of mutant lines for crop improvement.
Spontaneous and Induced mutations:
(1). Spontaneous mutation:
Mutation occurs in nature are called spontaneous mutation. Spontaneous mutation occurs in the organism without any treatment at low rate in the nature. The frequency of spontaneous mutation is 10-6 (one in 10 lakhs). Different genes in and organism show different mutation rate.
(2). Induced mutation:
Mutations induced in an organism by treatment with physical or chemical mutagen are called induced mutations. The agents which are used to induce mutation are called mutagens. Certain genes in an organism promote the mutation of other genes nearby in the chromosomes. For example, the gene Dt in Chromosome number 9 of maize increases mutation rate of other genes.
Characteristics of Mutation:
Ø Mutations are generally recessive; Dominant mutations do occur in nature.
Ø Mutations are generally harmful to organism; small percentage of mutation is beneficial.
Ø Mutation occurs at random in the chromosome, may occur in any gene.