Molecular basis of spontanceous mutation,induced mutation & physical and chemical mutagenes

1. MOLECULAR BASIS OF
SPONTANCEOUS
MUTATION,INDUCED MUTATION &
PHYSICAL AND CHEMICAL
MUTAGENES
Presented by:
Sumra Kazbanu A.
M.Sc sem-1
CBO-403
Department of life sciences
H.N.G.U. Patan

2. CONTENTS
Indroduction
Spontanceous mutation
Induced mutation
Physical mutagenes
Chemical mutagenes

3. Introduction
 What is mutataion?
 Some distinct variability is found between individual to
individual which may be passed on from one generation to
the next,must originate in some way .the process by which
these genetic changes occur is known as MUTATION.
 In 1791,Seth Wright,while studying his group of Sheep
with exceptionally short legs
 In 1901,Dutch Botanist Hugo de Vries,who for the first
time described such heritable changes from normal
triats.he named these changes as MUTATION.

5. SPONTANEOUS MUTATION
The Spontaneous mutations are considered as those
that arise naturally.No specific agent-other than
natural forces- is strictly by chance.
Although their origin is not fully understood,it is
believed that back-ground radiation from cosmic rays
and radioactive minerals account for many such
events

6. Spontaneous mutation rate = 1 in 109 (a billion)
replicated base pairs or 1 in 106 ( a million) replicated
genes. Mistakes occur during DNA Replication just
before cell division. This is natural error rate of DNA
polymerase.

8. INDUCED MUTATION
Induced Mutations Caused by mutagens. Mutagens
increase mistakes to 10–5 (100 thousand) or 10–3 ( a
thousand) per replicated gene.
In contrast to spontaneous mutation,those arising as a
result of the influence of any artificial factor are
considered to be induced mutations.

9. The earlist demonstration of the induction of
mutation occurred in 1927,when H.J.Muller reported
that X-rays could mutations in Drosophila.In 1928 ,
Lewis J.Stadler reported the same finding in barley.

10. Mutagens
Mutagens are things that cause mutations
– Radiation
• X rays, gamma rays break DNA, bases
• UV light causes knots in DNA strand
– Chemical mutagens
• Base pair changers (nitrous acid)
• Base analogues (e.g.. 5 bromouracil)
• Frameshift mutagens (aflatoxin, benzpyrene)

11. PHYSICAL MUTAGENES
The substances or agents,may be radiation
,temperature,which can induce or produce artificially
are called physical mutagenic agents.
I. Ionizing radiation (X rays, gamma rays, UV
light)
causes the formation of ions that can react with
nucleotides and the deoxyribose-

12. phosphate backbone.Nucleotide excision repairs
mutations.
Non-ionizing radiation:
Such a ultraviolet and visible light.

13. X-rays and Gamma Rays Cause Breaks
in DNA

14. UV radiation causes
thymine dimers,
which block
replication.
Light-repair
separates thymine
dimers
Sometimes the
“repair job”
introduces the
wrong nucleotide,
leading to a point
mutation.
Ionizing Radiation: UV
Figure 8.20

15. Temperature
The rate of all chemical reaction are influenced by
temperature.
It is reported that the rete of mutation is increased due
to increase in temperature.
Ex. An increase of 10C temperature increase the
mutation rate two or three fold.Temperature probably
affects both thermal stability of DNA and the rate of
reaction of other substances with DNA.

16. CHEMICAL MUTAGENES
Many chemical substances have been responsible to
increase the mutability of genes.
The ability of chemicals to induce mutation was first
of all demonstrate by Auerbach and Robson 1947
using mustard Gas and related compounds.the
nitrogen and sulphur mustards,mustards oil and
chloracetone in experiments with male drosophila
melanogaster.

17. melanogaster.
A chemical mutation can cause mutation only when it
enters in the nucleus of the cell.
Basae pir changers: deaminators like nitrous
acid, nitrosoguanidine, or alkylating agents like
cytoxan.
Base analogues: “mimic” certain bases but pair
with others - E.g. 5-fluorouracil, cytarabine

18. Chemical Mutagens:
Incorporated as a “T” Acts like a “C”
cytarabine
cytoxan
Nitrous acid

19. REFERENCES
GENETICS
BY: Suresh Kumar
Harshvardhan
www.google.com