genetics related topic important in studies at school and college level

1. MUTATION
Presented by:
RUPAL AGRAWAL
16SOSMB21001
SCHOOL OF SCIENCE
R.K.UNIVERSITY

2. INTRODUCTION:
• A mutation is the permanent alteration of the
nucleotide sequence of the genome of an
organism, virus, or extra chromosomal DNA or
other genetic elements.
• Most mutations are the result of error during
replication process/ error during DNA repair.
• CLASSES:

4. Types of Mutation:
1. Gene mutation
• Point mutation
- silent
- Mis-sense
- Non-sense
• Frameshift mutation
-Addition
- Deletion
2. Chromosome mutation
• Deletion
• Duplication
• Inversion
• Translocation
• Insertion

6. Silent mutation
Non-sense
mutation
Mis-sense
mutation

7. Spontaneous mutation:

10. The basis of mutational change: How do mutations arise?
If mutations are induced in
response to selection they will
occur only in the final generation
of cells – the ones that are
exposed to phage
If mutations occur randomly they
will occur throughout population
growth – i.e., prior to selection
grow up population
without selection (e.g.
no bacteriophage)
expose the population to
selection and count the
number of mutant individuals
(colonies)
Directed/Adaption hypothesis

11. LURIA- DELBRUCK EXPERIMENT
(Fluctuation test)
They tested that weather mutations are
independent of natural selection or they are
directed by the selection.

12. The basis of mutational change: How do mutations arise?
Luria and Delbruck started
populations of bacteria from a
small number of cells…
… and allowed them to grow up to
reach a large number of cells (~10
billion)
then determined the number of
bacteriophage resistant cells:
If the virus resistance is not due to
random gene mutation, then each
plate should contain the same number
of colonies.
Each level
represents a
round of cell
division
bacteriophage
on the plate kill
sensitive cells

13. Result:
• They found that the number of resistant
colonies on each plate varied drastically.
• CONCLUSION:
They proposed that these results could be
explained by the occurrence of a constant rate
of random mutation in each generation of
bacterial growth in the initial culture tube.

14. NEWCOMBE EXPERIMENT
This experiment was used to determine
wheather mutations which make E.coli
resistant to T2 phages are spontaneous or
whether exposure of the bacteria to the
phage induces the resistance to arise in cells.

15. 1. E.coli culture was examined and the colony
count of surviving colonies was counted.
2. One set of bacterial plate was exposed to T2
virus, and the other set was respread.
If mutations are induced by exposure to the T2
bacteriophage then approximately the same
number of mutants are expected to appear on each
plate, regardless of respreading the plate.
However, if the resistance to the T2 phage in E.coli
was a result of spontaneous mutations during cell
divisions prior to plating, then the respread plate
would be expected to have a higher number of
mutants.

16. OBSERVATION:
• It was observed that the unspread plate had
less T2 resistant colonies, while the respread
plate had more mutant colonies.
• This variation in the number of mutants on
each plate leads to the conclusion that the
mutation causing the resistance to
bacteriophage T2 in the E.coli arosed
spontaneously.

17. The Lederberg experiment
In 1952, Esther and Joshua Lederberg
performed an experiment that helped to
show that many mutations are random, not
directed.

18. • The hypothesis for the experiment is that
antibiotic resistant strains of bacteria surviving an
application of antibiotics had the resistance
before their exposure to the antibiotics, not as a
result of the exposure.
• Steps:
1. Bacteria are spread out on a plate,
called the "original plate.“
2. They are allowed to grow into
several different colonies.

19. 3. This layout of colonies is stamped
from the original plate on to a new
plate that contains antibiotic penicillin.
4. Colonies X and Y on the stamped plate survived.
They must carry a mutation for penicillin resistance.

20. RESULT:
• When the original plate is washed with penicillin, the
same colonies (those in position X and Y) live — even
though these colonies on the original plate have
never encountered penicillin before.
CONCLUSION:
• the penicillin-resistant bacteria were there in the
population before they encountered penicillin. They
did not evolve resistance in response to exposure to
the antibiotic.
So the mutations are random and not directed.