Author: SANDEEP KUMAR BANGARWA
- Mutation is the sudden heritable change other than the Mendelian segregation and gene recombination in an organism.
- Mutation Breeding :- When mutation are induced for crop improvement, the entire operation of the induction & isolation, etc of mutants is called mutation breeding.
- Mutation word is derived from the latin word ‘MUTARE’ means to change.
- Discovered by – Seth wright in male lamb with short legs (Ancon).
- In plants, first discovered by Hugo de vries in 1900 in Oenothera lamarckiana (Evening primrose). It was a hybrid plant.
- Term mutation coined by – Hugo de vries.
- Hugo de vries gave the evolutionary theory of mutation.
- Morgan first reported mutation in Drosophila (1910).
- Father of mutation – Morgan.
- Father of induced mutation- Muller.
- Muller (1927) first used x-ray for induction of mutation in drosophila.
- Stadler (1928) first used x-ray for induction of mutation in barley.
- Darwin gave the term sport for variations.
- Frameshift mutations are additions or deletions of nucleotides that cause a shift in the reading frame.
- Germline mutations occur in gametes. Somatic mutations occur in other body cells.
- Mutations are essential for evolution to occur because they increase genetic variation and the potential for individuals to differ.
- The majority of mutations are neutral in their effects on the organisms in which they occur.
- Beneficial mutations may become more common through natural selection.
- Harmful mutations may cause genetic disorders or cancer.
- Many genetic disorders are caused by mutations in one or a few genes. Other genetic disorders are caused by abnormal numbers of chromosomes.
- Plant breeding requires genetic variation of useful traits for crop improvement. Often, however, desired variation is lacking. Mutagenic agents, such as radiation and certain chemicals, then can be used to induce mutations and generate genetic variations from which desired mutants may be selected. Mutation induction has become a proven way of creating variation within a crop variety.
- It offers the possibility of inducing desired attributes that either cannot be found in nature or have been lost during evolution. When no gene, or genes, for resistance to a particular disease, or for tolerance to stress, can be found in the available gene pool, plant breeders have no obvious alternative but to attempt mutation induction.
1. Most of the mutant alleles are recessive but their normal alleles are dominant.
2. Induced mutations commonly show pleiotropy often due to mutation in closely linked genes.
3. Mutations are generally harmful to the organism but some mutations are beneficial.
4. Mutations are random.
5. Mutations are recurrent.
6. Mutations can occure in any tissue / cell or any developmental stages of an organism.
7. Rate of forward mutation is very high than rate of reverse mutation.
8. Physical and chemical agents increase the frequency of mutation, they are known as mutagens.
9. Mutations occur in both forward and reverse directions.
10. Spontaneous mutations occur at very low frequencies (10-4 ̶ 10-7 ) in nature without any known cause.
Classification of mutation
A. There are three types of mutations based on genetic basis of heritable change :-
1. Gene mutations
- These are produced by change in the base sequence of genes.
- The change may be due to base substitutions, deletion or addition.
2. Chromosomal mutation
- These arise due to change in chromosome number that may leads to polyploidy or aneuploidy or change in chromosome structure that result in deletions duplication, inversion and translocation.
3. Cytoplasmic or Plasmagene mutation
- These are due to change in the base sequence of plasma genes.
- The plasma genes are present in mitochondria or chloroplast.
- Here the mutant character occurrs in buds or somatic tissues which are used for propagation in clonal crops.
1 . Spontaneous mutations
- Mutations occur in natural populations at a low rate (10-6) but different genes may show different mutation rates.
- The different genes show different mutation rate.
- The difference in mutation rate may be due to Genetic back ground (i.e. presence of mutator genes), Genes them selves , Environment etc.
- Mutations may be artificially induced by treatment with certain physical or chemical agents.
- Induced mutation occur at a relatively higher frequency so that it is practical to work with them.
1. Macro mutations ( Oligogenic Mutation) -
- Large phenotypic effect and recognizable on individual plant basis and can be seen easily in M2 generations – Eg. Ancon breed in sheep.
- Small phenotypic effect which can not be recognized on individual plant basis but can be recognize only in a group of plants.
- Selection should be done in M3 or later generations.
1. Silent Mutation
Silent mutation causes no change in the activity of the protein; is ually the result of a substitution occurring in the third location of the mRNA codon. Because the genetic code is degenerate (most amino acids are coded for by several alternative codons), the resulting new codon may still code for the same amino acid.
2. Missense Mutation
A missense mutation is a nucleotide substitution that changes a codon so that it codes for a different amino acid in the protein. This usually results in a change of the activity of the protein. The change may be harmful or beneficial to the protein.
3. Nonsense Mutation
A nonsense mutation is the same as a missense mutation except the resulting codon codes for a STOP signal. The result is a premature termination of translation. The protein is shorter than usual (or nonexistent) and does not contain all the amino acids that it should. Therefore, this protein is most likely nonfunctional.
Applications of Mutation Breeding
1. Irradiation of interspecific (distant) hybrids has been done to produce translocations.
2. Mutation breeding has been used for improving both oligogenic as well as polygenic characters.
3. F1hybrids from intervarietal crosses may be treated with mutagens in order to increase genetic variability by inducing mutation and to facilitate recombination of linked genes.
4. Mutagenesis has been used to improve morphological and physiological characters including yielding ability.
5. Induction of desirable mutant alleles which may not be available in the germplasm
6. It is useful in improving specific characteristics of a well adapted high yielding variety.
7. Creation of New crop species.
8. Widening the genetic base of existing species.
1. Desirable mutations may be associated with undesirable side effects due to other Mutations.
2. Frequency of desirable mutations is very low .
3. Detection of recessive mutations in polyploids and clones is difficult and larger doses of mutagen have to be applied and larger populations are to be grown.
4. To screen large population, efficient quick and unexpensive selection techniques are needed.
1. Phundan Singh, 2006. Essentials of Plant Breeding . Kalyani Publishers, New Delhi.
2. Singh, B.D. 2012. Plant Breeding: Principles and Methods. Kalyani Publishers, New Delhi
About Author / Additional Info:
I am currently pursuing Ph.D. in Plant Breeding and Genetics from MPUAT-Udaipur (Raj.)