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Mutation Breeding in Agricultural Sciences
- 1. MUTATION BREEDING INCROP IMPROVEMENT Mutation: Sudden heritable change in a characteristic of an organism (Gene, Chromosome (s) or plasmagene) Historical Account • The term mutation was first coined by Hugo de Vries (1900). Evening prime rose (Oenothera lamarkiana). •Muller (1927): Mutagenic actions of X-rays on Drosophila •Stadler (1928): Mutagenic actions of X-rays & gamma-rays in Barley and Maize
- 2. DEFINITIONS Mutation : Suddenheritable change in a characteristic of an organism (Gene, Chromosome (s) or plasmagene). Mutant: Product of mutation. It may be a genotype, a cell or a polypeptide. Muton: The unit of mutation, the smallest unit gene (DNA) capable of undergoing mutation. Mutagen: Physical or chemical agents which greatly enhance the frequency of mutation.
- 3. CHARACTERISTICS OF MUTATIONS Mutationsare generally recessive Generally harmful to the organism Random i.e. they may occur in any gene Recurrent: same mutations may occur again and again Induced mutations commonly show pleiotropy (closely linked genes)
- 4. TYPES OF MUTATIONS I.Types of cells in which mutation occurs. a) Somatic mutations : Mutations occurring in body cells. These are not transmitted to next generation and hence termed as non-heritable mutations. b) Germinal mutations : Mutations occurring in reproductive cells and such mutations are heritable and passed on to next generation II. Mode of Origin a) Spontaneous mutations or Natural Mutations : Mutations occur naturally (10-6 ) b) Induced mutations : Produced artificially in the laboratory.
- 5. III. Based onSurvival • Lethal: They kill each & every individual that carry them in appropriate genotype . Dominant lethal : It can’t survive. Recessive lethal : kill in homozygous state. Sub Lethal & Sub Vital : Both mutation reduce viability but don’t kill all the individual carrying them in appropriate genotype. Sub Lethal : Kill more than 50%. Sub Vital : Kill less than 50%. Vital : a) Don’t reduce the viability. b) Used in Crop improvement Cont…
- 6. Cont… IV. Mutations basedon their directions a) Forward mutation : Wild type (normal type) Mutant type b) Reverse mutation - Backward mutation Mutant type Wild type (normal type V. Type of genes Involved a) Macro (Oligo mutations / Qualitative Mutations) Phenotypic effect is quite clear e.g. clour, shape etc. b) Micro Mutations (Polygenic mutations) Phenotypic effects are invisible, need large populations to score mutations and special statistical analysis is required to detect their effect (biometrical techniques) e.g. change in yield, plant height etc.
- 7. 1. Nuclear Mutations a.Gene mutation or Point mutation Mutations produced by changes in the base sequences of genes are known as gene or point mutations. b. Chromosomal mutations : Mutations may cause changes in the structure of chromosome or even in chromosome number. 2. Cytoplasmic mutations : Mutations that occur in cytoplasmic DNA VI. Based on Site Cont…
- 8. Point mutations: changein base sequence of DNA I. Base Substitution II. Base addition or deletion 1. Base Substitution: one base in a DNA molecule is replaced by another one Transitions: Replacement of one purine by another purine or one pyrimidine by another pyrimidine Transversions: Substitution of a purine by a pyrimidine or vice versa POINT MUTATION PURINES PURINES PYRAMIDINES PYRAMIDINES PURINES PYRAMIDINES TRANSITION TRANVERSION A G T C A T/C G T/C
- 9. Codons which resultedoften from base substitution fall into three categories 1. Sense codons : Which are read or translated the same as before mutation. Ex: CUU, CUC- Leucine; CCU, CCC- Proline 2. Missense codons : Which code for a different amino acid. Ex: CUU- Leucine ; CCC- Proline 3. Nonsense codons: code for no amino acid (terminator of polypeptide chain) Ex: UAA, UAG, UGA
- 10. II. BASE ADDITIONAND DELETION Base Addition: Insertion of one/more bases in a DNA molecule Base Deletion: Loss of one/more bases in a DNA molecule Frame shift mutations Mutations arise from the insertion (+) or deletion (-) of a nucleotide or nucleotides into or from DNA molecule. The reading frame is shifted from the point of addition/deletion
- 11. A T CG A C A T C T T C C T C A A T C G A C C A T C T T G C T A T C G A C T C T C T C T C C ….. 1 4 2 3 5 1 7 2 6 8 G 1 9 2 3 10
- 12. Mutagenic Agents Chemical Physical 1.Alklalyting agents -EMS, MMS, DES 2. Acridine dyes - Ethidium Bromide 3. Base analogues - Bromo Uracial 4. Others - Nitrous acid, Sodium Azide Ionizing radiations Non Ionizing radiations UV Rays Particulate Non Particulate Alpha Rays, Fast Neutrons X-Rays, Gamma Rays
- 13. Physical mutagens Irradiation: Exposureof biological material to radiations mainly to mutation causing radiations Ionizing Radiations: Radiations which produce ions in the medium through which they pass Particulate Radiations: Radiations which emit particles when pass through a medium Ionization: loss or gain of an electron by an atom Excitation: Movement of an electron to an outer orbit of higher energy level Tautomerization: shift of H atom from one position to another either in a purine/pyrimidine base
- 14. Type of Radiation Properties Sourceof production Mode of action Remarks X- rays (Roentge n) S.I., Penetrating & non- particulate X ray tubes/machi nes Induce mutations by forming free radicals & ions. Cause addition, deletion, transistions & transversions Widely used for induction of mutations in various crop plants Gamma rays S.I., very penetrating & non- particulate Radioactive decay of elements like 14C, 60C, radium By ejecting atoms from the tissues. Cause addition, deletion, transistions & transversions --Do-- Alpha particles D.I., Particulate, +ve charged Emitted by the isotopes of heavier elements Ionization & excitation. Chromosome breakage & gene mutations Rarely used
- 15. Type of Radiation Properties Sourceof production Mode of action Remarks Beat rays S.I., Particulate, -ve charged Radioactive decay of heavier elements (3H, 32P,35S) Ionization & excitation. Chromosome breakage & gene mutations Rarely used Fast & Thermal neutrons D.I., Particulate, neutral Radioactive decay of heavier elements in atomic reactors Chromosome breakage & gene mutations Asexual crops UV rays Non ionizing, low penetrating Mercury vapour lamps or tubes Chromosome breakage & gene mutations Micro- organisms & radiation of pollens
- 16. 1.Alkylating agents: Chemicalmutagens which cause mutations by adding alkyl group at various positions in DNA Radiometric chemicals EX: Ethyl Methane Sulphonate (EMS), Methyl Methane Sulphonate (MMS) 2. Base analogues: Compounds similar to DNA Bases Ex: 5 Bromo Uracil ( BU), 2 Amino Purine (2 AP) 5BU= Thymine 3. Acridine dyes: They get inserted between two bases of DNA and lead to additioin/deletion of base pairs (Frameshift mutations) Ex: Proflavine, Acridine orange, Ethidium Bromide Chemical Mutagens
- 17. Mutation breeding :Thegenetic improvement of crop plants for various economic traits through the use of induced mutations Used in S.P. and clonally propagated crops. Mutation breeding is successful when…… Desired variability exhausts in cultivated species and germplasm. When a desirable variety has an oligogenic genetic defect. There is tight linkage between desirable and undesirable traits. Only one or two characters are to be improved in a fruit crop without changing its taste. Crop does not have sexuality, thus lacks variability. The generation cycle is very long, such as plantation crops, fruit tree In ornamental plants MUTATION BREEDING
- 18. A particular reactionis to be blocked E4 E3 E2 E1 E6 E5
- 19. PROCEDURE OF MUTATIONBREEDING Mutagenesis : Treating a biological material with a mutagen. Irradiation : Exposure of biological material to one of the radiation 1. Choice of the material/Variety Usually the locally adapted best variety will be selected. 2. Choice of mutagen Chemical mutagens: Seed treatment Physical mutagens: Treatment of vegetative parts (penetration) 3. Mutagenic Treatment 1. Plant species A. Sexually propagated – Seeds/ Pollen grains B. Asexually propagated: Buds, Cuttings, Suckers C. Complete Plant
- 20. 2. Dose ofmutagen: LD50 LD50: dose of mutagen that kills 50% of the treated individuals 3. Duration of treatment: Concentration of chemical mutagens/Intensity of radiations Sexually propagated crops : Seeds are commonly used because seed can tolerate extreme environmental conditions. Pollen grains are infrequently used They are difficult to collect in large quantities . Hand pollination (with treated pollens) is rather difficult. Survival percentage of pollens is relatively low. Note:- Pollen grains are the only plant part which can be treated with ultra violet rays
- 21. Giving mutagen treatment Irradiation:BARC, Mumbai In irradiation the plant parts are immediately planted to raise M1 plants from them. Chemicals: In case of chemical mutagens seeds are usually soaked for few hours to initiate metabolic activities. Then they are washed under running tap water. After this they are planted in the field to raise M1 generation.
- 22. The chimera refersto genetically different tissue in an individual. OR The individual has one type of tissue in one part and another type of tissue in another part. CHIMERA
- 23. Shoot Tip Meristem L1:Epidermis L2: Produces a part of mesophyll & gametes L3: rest of plant body Shoot Tip Structure
- 24. L1 L2 L3 Shoot Tip Initial AA AA AA AA AA AA AA AA AAAA AA AA AA AA Aa Aa Aa Aa Sectorial L2 Sectorial L3 Periclimal L2 Periclimal L3 2. Periclinal chimera: Whole of L1, L2 or L3 layer is affected 1. Sectorial chimera: Part of L1, L2 or L3 layer is affected Types of Chimeras
- 25. Treated seeds Pollination withthe Treated pollens M1 plants : Plants obtained from treated seeds/cuttings or from seeds obtained after pollination with treated pollens are called M1 plants M1 Plants
- 26. Treated seeds arespace planted Individual plants are harvested separately Individual plant progenies grown Superior mutant lines are harvested in bulk if they ate homogeneous Individual plant progenies grown Mutant plants are harvested separately Preliminary yield trial with check Superior lines are selected Replicated yield trial at several locations Superior lines are released as variety Seed multiplication and distribution M1 M5- M7 M4 M3 M2 M8
- 27. ADVANTAGES New genotypes thatare not present in germplasm can be created artificially. Specific characters can be improved in a variety which may be either qualitative or quantitative. For induction of male sterility induced mutagenesis can be used. Ex. Ethidium Bromide-CMS in Barley and Pearl millet Cheap & rapid method of developing new varieties (BC, PB,BB) Vegetatively propagated crops: induction of variability
- 28. LIMITATIONS •Most of themutations are deleterious and undesirable • Hit or miss method. • Identification of the micro-mutations is very difficult • Frequency of useful mutations is very low (0.1%). Large populations are to be screened. • Desirable mutants may be associated with other undesirable traits. • Most of the mutants are recessive. Recessive mutants cannot be identified in clonally propagated crops. • Limited scope for the genetic improvement of quantitative traits. • Mutations in quantitative traits are usually in the direction away from the selection history of the parent variety.
- 29. Applications in cropimprovement 1. Development of Improved varieties Castor : Aruna Rice : Jagannath Groundnut : Co2 Red gram ` : Co5 Cotton : MCU 10. Black gram : Co 4 2. Induction of Male sterility: Ethidium Bromide- CMS in Wheat, Barley Pearl millet 3. Production of Haploids: X-ray irradiated pollens has helped in production of haploids in many crops 4. Creation of variability: Asexual crops (Sugar cane, potato & Flower crops) 5. Overcoming Self Incompatibility