Mutation Breeding in Agricultural Sciences

Mutation

1. MUTATION BREEDING IN CROP 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-rayson Drosophila
•Stadler (1928): Mutagenic actions of X-rays & gamma-rays in
Barley and Maize

2. DEFINITIONS
Mutation :Sudden heritable 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
Mutations are 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 on Survival
•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 based on 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:change in 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
POINTMUTATION
PURINES
PURINES
PYRAMIDINES PYRAMIDINES
PURINES PYRAMIDINES
TRANSITION
TRANVERSION
A G
T C
A T/C
G T/C

9. Codons which resulted often 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 ADDITION AND 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 AT CT T CC T C
A
A T CG A C C A TC T TG C T
A T CG A C T C TC T C T C
C …..
1 42 3 5
1 72 6 8
G
1 92 3 10

12. MutagenicAgents
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 radiationsNon Ionizing radiations
UV Rays
Particulate Non Particulate
Alpha Rays, Fast
Neutrons
X-Rays, Gamma Rays

13. Physical mutagens
Irradiation:Exposure of 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
PropertiesSource of
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 Source of
production
Mode of actionRemarks
Beat raysS.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 raysNon ionizing,
low penetrating
Mercury
vapour
lamps or
tubes
Chromosome
breakage &
gene mutations
Micro-
organisms &
radiation of
pollens

16. 1.Alkylating agents:Chemical mutagens 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 :The genetic 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 reaction is to be blocked
E4
E3
E2E1
E6E5

19. PROCEDURE OF MUTATION BREEDING
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 of mutagen: 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. Givingmutagentreatment
Irradiation:BARC,Mumbai
InirradiationtheplantpartsareimmediatelyplantedtoraiseM
1
plantsfromthem.
Chemicals:
Incaseofchemicalmutagensseedsareusuallysoakedforfew
hourstoinitiatemetabolicactivities.
Thentheyarewashedunderrunningtapwater.
AfterthistheyareplantedinthefieldtoraiseM
1generation.

22. The chimera refers to 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
AA
AA
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 with the Treated pollens
M1 plants:Plants obtained from treated seeds/cuttings or from seeds
obtained after pollination with treated pollens are called M
1plants
M
1Plants

26. Treated seeds are space 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
M
1
M
5-M
7
M
4
M
3
M
2
M
8

27. ADVANTAGES
New genotypes that are 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 the mutations 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 crop improvement
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