Document

1. Mutations
MD MAHIDUL ISLAM
MSc, PGD

2. What is a gene mutation?
Mutations are changes in genetic material – changes in
DNA code – thus a change in a gene(s)
In gene mutations, the DNA code will have a base (or more)
missing, added, or exchanged in a codon.
2

3. How common are mutations?
Mutations occurs at a frequency of about 1 in every 1 billion base
pairs
Everybody has about 6 mutations in each cell in their body!

4. Classification of mutation
A. Based on the survival of an individual:
1.Lethal mutation – when mutation causes death of all individuals
undergoing mutation are known as lethal
2.Sub lethal mutation - causes death of 90% individuals
3.Vital mutation - when mutation don’t affect the survival of an individual are
known as vital
4.Supervital mutation – This kind of mutation enhances the
survival of individual

5. 5
B. Based on causes of mutation:
1.Spontaneous mutation-
Spontaneous mutation occurs naturally without any cause. The rate of spontaneous mutation is very
slow eg- Methylation followed by deamination of cytosine.
Rate of spontaneous mutation is higher in eukaryotes than prokaryotes.
Eg. UV light of sunlight causing mutation in bacteria.
2.Induced Mutation-
Mutations produced due to treatment with either a chemical or physical agent are called induced
mutation .
The agents capable of inducing such mutations are known as mutagen. use of induced mutation for
crop improvement program is known as mutation breeding.
Eg. X- rays causing mutation in cereals

6. C. Based on tissue of origin
1.Somatic mutation-
A mutation occurring in somatic cell is called somatic mutation.
In asexually reproducing species somatic mutations transmits from one
progeny to the next progeny
2.Germinal Mutation-
When mutation occur in gametic cells or reproductive cells are known as
germinal mutation.
In sexually reproductive species only germinal mutation are
transmitted to the next generation

7. Mutations are a major source of genetic
variation in a population increasing
biodiversity.
Some variations may help them to
survive better.
How do mutations affect a population?

8. Types of Mutations

9. Types of Chromosome Mutations
• May Involve:
–Changing the structure of a
chromosome
–The loss or gain of part of a
chromosome

10. Chromosome Mutations
• Five types exist:
– Deletion
– Inversion
– Translocation
– Nondisjunction
– Duplication

11. Deletion
• Due to breakage
• A piece of a chromosome is
lost

12. Inversion
• Chromosome segment
breaks off
• Segment flips around
backwards
• Segment reattaches

13. Duplication
• Occurs when a gene sequence is
repeated

14. Translocation
• Involves two chromosomes that are
NOT homologous
• Part of one chromosome is
transferred to another
chromosome

15. Nondisjunction
• Failure of chromosomes to separate during meiosis
• Causes gamete to have too many or too few chromosomes
• Disorders:
– Down Syndrome – three 21st chromosomes
– Turner Syndrome – single X chromosome
– Klinefelter’s Syndrome – XXY chromosome

17. Chromosome Mutation
Animation

18. Types of Gene Mutations
Point mutation occurs when the base sequence of a codon is
changed. (ex. GCA is changed to GAA)
There are 3 types:
•Substitution
•Deletion
•Insertion
Also called
frameshift
mutations

19. Substitution Mutations
Mutated DNA: CGA – TGC – TTC
Normal DNA: CGA – TGC – ATC
Alanine – Threonine - stop
Alanine – Threonine - Lysine
What has happened to the DNA?

20. Substitution Mutations
Alanine – Threonine - Lysine
Mutated DNA: CGA – TGC – TTC
This is a substitution mutation.
A single nitrogen base is substituted for
another in a codon.
It may or may not affect the amino acid or
protein.
Normal DNA: CGA – TGC – ATC
Alanine – Threonine - stop
20

21. Substitution Mutations
Base substitutions can be divided into two
subtype:
Transition mutation
A transversion is the opposite the replacement of a base of one
chemical category by a base of the other
Purine Purine
A > G , G > A
Pyrimidine Pyrimidine
T > C , C > T
Transversion mutation
A transversion is the opposite the replacement of a base of one
chemical category by a base of the other.
Purine Pyrimidine
A > C, A >T , G > C , G > T
Pyrimidine Purine
T > A, T > G, C > T, C
21
> G

22. Insertion Mutations
Normal DNA: CGA – TGC – ATC
Alanine – Threonine – stop
Mutated DNA: CGA – TAG – CAT – C
Alanine – Isoleucine – Valine

23. Insertion Mutations
Mutated DNA: CGA – TAG – CAT – C
Alanine
23– Leucine - Valine
This is an insertion mutation.
A nitrogen base is inserted/added to
the sequence.
It causes the triplet “frames to shift”.
It always affects the amino acids and
consequently the protein.
Normal DNA: CGA – TGC – ATC
Alanine – Threonine - stop

24. Normal DNA: CGA – TGC – ATC
Alanine – Threonine – stop
Mutated DNA: CGA – TCA- TC
Alanine – Serine
Deletion Mutations

25. Deletion Mutations
This is a deletion mutation.
A nitrogen base is deleted/removed from the sequence.
It causes the triplet “frames to shift
It always affects the amino acids and consequently the protein.
Normal DNA: CGA – TGC – ATC
Alanine – Threonine – stop
Mutated DNA: CGA – TCA- TC
Alan2
in
5 e – Serine

26. Frameshift Mutation
 Inserting or deleting one or more nucleotides
 Changes the “reading frame” like changing a sentence
 Proteins built incorrectly

27. CLASSIFICATION OF POINT MUTATIONS
DEPENDING ON EFFECTS
MUTATION:
• Missense mutation
• Silent mutation
• Non-sense mutation

28. MISSENSE MUTATION:
• The new codon causes an incorrect AMINO ACID to be inserted into
the protein.
• This effect on the function of the protein depend on what is inserted in
place of normal amino acid.
28

30. NON-SENSE MUTATION:
When a base substitution results in a stop codon
ultimately truncating translation and most likely
leading to a nonfunctional protein.

32. SILENT MUTATION:
Silent mutation does not causes any change in amino acid.
(Silent mutation codes for same amino acid)
DNA:
mRNA:
> TTC
AAG
TTT
AAA -
Lysine - Lysine

33. 33