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1. Gene Mutation
By
Tabinda Jabeen

2. •Mutation
• The term ‘mutation’ was introduced by Hugo De
Vries in evening prime-rose (Oenothera
lamarckiana).
• It is a sudden, hereditary change in the genetic
make up of an organism.
•Mutagens
• Mutagens are the agents inducing mutation.
• There may be chemical or physical mutagens.
Oenothera lamarckiana

3. • 1. Chemical Mutagens:
Further classified as:
1. Base analogues
• Analogous to nucleotide
bases.
• Ex. ‘-5 bromo-uracil’ &
‘-2 amino-purine’ are
analogues of thymine.
• Appear as actual bases
but in fact they are not.
2. Alkylating agents
• Add an alkyl group
(CnH2n+1) to nucleotide
base.
• Induce changes in base
pairing.
• Ex. Ethyl-methane
Sulphonate converts
guanine to 7-
ethylguanine which then
pairs with thymine
instead of cytosine.
3. Acridines
• Positively charged
molecules.
• Inserted between two
DNA strands, thereby
altering DNA's structure
and rigidity.
• Disturbing DNA
replication.
• Ex. Proflavin.

5. Physical Mutagens:
• Mostly radiations.
• Two classes;
1. Ionizing radiations
• Highly energetic and
penetrative.
• Damages DNA by ionizing the
atoms present in it.
• Ex. X-rays, α-radiations, β-
radiations and ɣ-rays.
2. Non-ionizing radiations
• Electromagnetic radiation with
wavelength from 10-400 nm.
• Interferes directly with the
bonding between the
nucleotides.
• Formation of thymine dimers.
• Prevents normal replication
and transcription.

6. Classification of mutation
Criteria Classes
On the basis of location 1. Chromosomal mutation
2. Gene mutation
On the basis of type of cells 1. Somatic mutation
2. Germinal mutation
On the basis of cause 1. Spontaneous mutation
2. Induced mutation
On the basis of out-come
(result)
1. Same sense
2. Anti-sense
3. Non-sense

7. •Classification # 1: On the basis of location
1. Chromosomal mutation:
• Occurring in chromosomes.
• In number of structure.
•
2. Gene Mutation:
• Occurring in genes.
• Further classified into three categories;
1) Point Mutation
2) Inversion mutation
3) Frame-shift mutation

8. 1. Point Mutation
• A change/ alteration at a single base.
• Ex. Sickle cell anemia.
• Normally, amino acid at 6th position has
genetic code ‘GAG’ coding for glutamic
acid.
• After mutation, ‘GAG’ is converted to
“GTG’, now coding for valine.
Gene Mutation

9. 2. Inversion Mutation
• Adjacent bases in genetic code are flipped by 180 degrees.
• Ex.
• Normal chain: GGC-TCC-TCA-CGC-CAG
• Mutant chain: GGC-CTC-TCA-CGC-CAG
• Both point and inversion mutation only change a single amino acid in the
chain.
• All other amino acids of the chain are not disturbed.
Glutamic acid
Glycine

10. • 3. Frame-shift Mutation
• Whole chain is disturbed due to change in single code.
• In order to understand it, a statement is given here, (keep in mind it is only for the
sake of understanding the concept and you are not supposed to write it in paper).
WHYDIDTHECATEATTHERAT
(normal chain)
• In this sentence all words have 3 alphabets, assume them as triplet
genetic codes and make complete sense (WHY, DID etc.. )
• Now if there is a change in any single code, the whole chain (before &
after that code) will be disturbed.

11. • Case #1: Addition of nucleotide base
• WHYDIDTHECATEATTHERAT---- Normal
• WHYADIDTHECATEATTHERAT---- mutant
• New codes are; WHY, ADI, DTH, ECA,TEA,TTH,ERA,T-
• Case #2: Deletion
• WHYDIDTHECATEATTHERAT---- Normal
• W_YDIDTHECATEATTHERAT----- mutant
• New codes are; WYD, IDT, HEC, ATE, ATT, HER, AT-
• In both cases, the whole chain is disturbed, before and after the
location of change.
• All amino acids produced by these codes will be different from the
normal chain.

12. •Classification # 2: On the basis of type of cells in
which mutation occurs:
1. Somatic
• In somatic/ vegetative/ body cells.
• Other than reproductive parts.
• Not inherited.
• Ex. Skin cancer.
2. Germinal
• In cells of germinal epithelium
present in gonads.
• Reproductive parts.
• Inherited from parents to offspring.
• Ex. Sickle-cell anemia

13. •Classification # 4: On the basis of cause
1. Spontaneous
• Rare, occur due to natural
causes, without human
interference
• Mostly by errors in DNA
replication
• By exposure to natural
influences, such as radiation
or chemical agents in
environment.
2. Induced
• Purposefully done by man
by exposure to mutagens.
• Desired characters are
induced in the genome of
mutants.
• Exploitation of induced
mutations for crop
improvement is called
mutation breeding.

14. Classification # 5: On the basis of out-come/result:
1. Same Sense
• GAG--- Normal
• GCG--- mutant
• But both codes for
glutamic acid.
• Mutation occur but
no change in result/
outcome.
2. Anti-sense
• GAG--- normal
(glutamic acid)
• GUG--- mutant
(valine)
• A different amino
acid is produced.
3. No-sense
• Mutation result in
stop codon.
• GAG--- glutamic
acid
• UAG--- non-sense
(stop codon)
• No amino acid is
produced.

15. Few important terminologies:
• Muton: The smallest unit of gene capable of undergoing mutation and
it is represented by a nucleotide.
• Mutator gene: A gene which causes another gene or genes to undergo
spontaneous mutation.
• Mutable genes: Genes which show very high rates of mutation as
compared to other genes.
• Mutant: An organism or cell showing a mutant phenotype due to
mutant allele of a gene.
• Mutagen: A physical or chemical agent which induces mutation.
• Hot spots: Highly mutable sites with in a gene.

16. THE END