DEPARTMENT OF PLANT BREEDING AND GENETICS

1. Doctoral Seminar (GP 692) on
Molecular Mechanisms of Mutation, repair and Suppression
Presented by
DEEPAK SARAN
Ph.D. Scholar
Dept. of Genetics &
Plant Breeding
IGKV
2020-2021

2. CONTENTS
• INTRODUCTION
• BASIC TERMINOLOGIES
• FEATURES OF MUTATION
• TYPES OF MUTATION
• MOLECULAR BASIS OF MUTATION
• MOLECULAR MECHANISMS OF MUTATION
• REPAIR
• SUPPRESSION
• CASE STUDY

3. INTRODUCTION
A mutation is a change or alteration happens in a DNA, gene
or chromosome due to intrinsic or extrinsic factors such as an
error in replication or exposure to UV light, respectively.
• Change in the nucleotide sequence of the DNA”, is a mutation.
• The mutation is an important biological process in nature.
• The word mutation was similar to the French word “mutacioun” which literally means
“process of changing.”
• Although the “mutation” world was originally derived from the Latin word “mutare”.
The meaning of this is “to change.”

4. What is Mutation?
• Sudden heritable changes in genetic material is known as Mutation
The term Mutation refers both to
•Change in genetic material &.
•To the process by which the change occurs.

5. WITHOUT MUTATION
• All genes would exist in one form
• Alleles would not exist
• Genetic analysis would not be possible
• Not able to evolve & adapt to environmental
changes

6. BASIC TERMINOLOGIES
• MUTATION
• MUTAGEN
• MUTANT
• SPONTENEOUS MUTATION
• INDUCED MUTATION
• POINT MUTATION
• FRAMESIFT MUTATION
• MISSENCE MUTATION
• NON-SENCE MUTATION
• SILENT MUTATION

7. FEATURES OF MUTATION
.
SUDDEN
AND
HARITABLE
Permanent
structural
changes
Recessive
in nature
Recurrent
in nature
Pleotropic
effect
Mostly
deleterious
and rarely
beneficial
Reverse and
forward
Random
change
Low
frequencies
Spontaneous
and induced

8. TYPES OF MUTATIONS
SPONTENEOUS MUTATION
• naturally occurring mutations
and can arise in any cells.
• Occurs in nature without any
known cause
• Prokaryotes - 10-5 to 10-7 and
Eukaryotes - 10-4 to 10-7 d
• Example – loss of the hard seed
coat and other germination
inhibitors (dormancy) in wheat,
barely and peas
INDUCED MUTATION
• resulting from exposure of
organisms to physical and chemical
agents (mutagens) that cause
changes in DNA.
• Example
• Physical mutagen – fast neutron in
Rice (3-8 GY) AND Wheat (2-6 GY)
• Chemical mutagen-EMS in Rice(0.2-
0.5%)-8-20h(Malaszyanki et al
2009)

9. MOLECULAR BASIS OF MUTATIONS
BASE SUBSITUTION BASE ADDITION OR
DELTION
TRANSPOSTION TRINUCLEOTIDE
REPEAT EXPANSION
Example - Fragile X
syndrome, common form
of mental retardness,
results from change in the
number of (CGG)n
repeats in region of FMR-
1 gene that is transcribed
but not translated.
Examples : Mendel’s
wrinkled allele in the pea.
The first mutation (w1)
causing white eyes in
Drosophila (resulted from
the insertion of
transposable elements).

10. Errors in the
DNA
Replications
Tautomeric
Shift
Specific
Mispairing
Intercalating
Agents
Spontaneous
Lesions Base Analogs Base Damage

11. TAUTOMERIC SHIFTS
• Watson and Crick pointed out that the specific base pairing and structures of the bases
in DNA are not static, Hydrogen atoms and Amino nitrogen shifts their position known
as TAUTOMERIC SHIFTS.

12. Errors in the DNA Replications

13. SPONTANEOUS LESIONS
DEPURINATION DEAMINATION
OXIDATIVELY DAMAGED BASES
The linkage between a purine
and deoxyribose can
spontaneously
break. If not repaired, this can
lead to mutation.
Cytosine or 5 methyl
cytosine can spontaneously
deaminate to create uracil
or thymine.
Cause oxidative damage
to DNA, also to precursors
of DNA (such as GTP),
resulting in mutation.

14. Some potent chemical mutagens.

15. HNO2
UV Rays

17. Repair Mechanisms
LIGHT-DEPENDENT REPAIR
EXCISION REPAIR
the error-prone repair system (SOS response).
mismatch repair
postreplication repair

18. LIGHT-DEPENDENT REPAIR
• Light-dependent repair or photo reactivation of DNA in bacteria is carried out by a light
activated enzyme called DNA photolyase

19. EXCISION REPAIR
• Excision repair of damaged DNA involves at least three
steps.
• In step 1 :- a DNA repair endonuclease or endonuclease-
containing enzyme complex recognizes, binds to, and
excises the damaged base or bases in DNA.
• In step 2 :- a DNA polymerase fills in the gap by using the
undamaged complementary strand of DNA as template.
• In step 3:- the enzyme DNA ligase seals the break left by
DNA polymerase to complete the repair process

20. OTHER DNA REPAIR MECHANISMS
Mismatch repair in E. coli Repair of a double-strand break in DNA

21. Repair of a double-strand
break in DNA via
homologous
recombination repair.

22. • A suppressor mutation is a mutation that counters the phenotypic effect of a previous
mutation.
• It may either alleviates or reverts the phenotypic effects of an already existing
mutation.
• Genetic suppression therefore restores the phenotype seen prior to the original
background mutation.
• For example, say a mutation causes the codon 'AGA' (which codes for the amino acid
Arginine) to change to 'AGC' (which codes for the amino acid Serine, a very different
amino acid to Arginine). A suppressor mutation may be one that changes the mutated
codon to 'CGC' (which also codes for Arginine), or to 'AAG' (which codes for Lysine, a
similar amino acid to Arginine), thereby reversing the effect the first mutation may
have had on the function of the protein.

23. Mechanisms of suppression

24. Examples of Suppressor Mutations

25. Examples of Suppressor Mutations

26. Examples of popular induced mutants in crop plants are:
CROP MUTANT VARIETY ORIGINAL VARIETY MUTAGEN USED
Rice Jagannath
Mahsuri mutant
T-141
Mahsuri,
X-rays
g-rays
Wheat Sharbati sonara
NP-836
Sonara 64
NP-799
UV rays
x rays
French Beans Pusa Parvati
Pusa Lal Meeruti
Wax podded
Meeruti
x-rays
x-rays
Tomato S-12 Sioux g-rays
Castor Aruna HC-6 Thermal
neutrons
Cotton MCU 7
MCU 10
1143 EE
MCU 4
x-rays
g-rays

27. CASE STUDY

28. Objectives of the study
• To investigate the role of phosphorylation
• subsequent nuclear localization of PTEN with DNA
repair.
• Using PTEN deficient U87MG cells
Methodology
• MTT assay
• Fluorescence microscopy
• Western blotting and immunoprecipitation
• Comet assay
• Statistical analysis with Origin Pro v.8
software
Results from MTT assay
Percentage of survivability is lowered in all
transfected cells compared to
untransfected cell
Conclusion
• DNA damage augments phosphorylation of PTEN.
• Nuclear accumulation of PTEN increases which positively
regulates the DNA repair process.
• PTEN as the intermediate component of DNA repair.
• Phosphorylation of PTEN is associated with DNA repair