0.1 What are viruses? 1. Origin of viruses 1.1 introduction 1.2 Theories RNA molecules that existed before cells cell components micro-organisms. 1.3 Conclusion: How did viruses originate?

1. WELCOM
E

2. VIRUSES ORIGIN AND
EVOLUTION
ELHALABI HASAN
CHEBAT DIMA
SUPERVISION: DR. F. MONEM,
VIROLOGY
PhD

3. TABLE OF CONTENTS SECTION 1
•0.1 What are viruses?
•1. Origin of viruses
• 1.1 introduction
• 1.2 Theories
• RNA molecules that existed before cells
• cell components
• micro-organisms.
• 1.3 Conclusion: How did viruses originate?

4. TABLE OF CONTENTS
• 2. Evolution of viruses:
• 2.1 Introduction
• 2.2 Evolution drivers:
• 2.2.1 Progeny
• 2.2.2 Mutation
• 2.2.3 Quasispecies effects
• 2.2.4 Selection
• 2.7 Evolution in 2012
• 2.8 Conclusion

5. WHERE DID VIRUSES COME FORM?
THE MAIN QUESTION NEEDS TO BE
ANWERED IS:

6. WHAT ARE VIRUSES?
• Parasites, selective infection.
• Living or not?
• Genetics:
• RNA viruses
• DNA viruses
• Structure:
• Capsid
• Genome

7. 1.1 INTRODUTION
• Where did viruses come from?
• Fossils-origin relationship.
• Speculation on how viruses may have
orginated.
• How old are Viruses? Related to
Bacteria?
• The age of Eukaryotic viruses vs. the
age of prokaryotic?

8. TIME LINE OF EARTH HISTORY

9. THEORIES ON THE ORIGIN OF VIRUSES
• 1. Molecular precursors of cellular organisms
• 2. Components of cells
• 3. Intracellular micro-organisms.

10. 1. MOLECULAR PRECURSORS OF
CELLULAR ORGANISMS
• RNAs were originated before cells
and had many features.
• What happened as cells evolved?

11. 2. COMPONENTS OF CELLS
• 1. Independent from host cell
control, components could
replicate?
• 2. Structural similarities between
mRNA and some viruses.
Covalently:
• 3. Could some DNA viruses be
descendant of plasmids?
• 4. Or Transposons maybe?

12. 2. COMPONENTS OF CELLS
• 5. Are we made of viruses?:
• Chicken-and-egg situation
between
retrotransposons and
retroviruses!!
• HGSP: 8% of genom is LTR-flanked

13. 3. INTRACELLULAR M.O.
• degeneracy of intracellular M.O. until the it becomes a virus?

14. CONCLUSION:
THE MAIN QUESTION’S STILL UNANSWERED
• Multiple sugessted ancestors, unknown origin
• Many processes may have participated
• Viruses selectivity to host may refer to the origin.

15. Evolution is the constant change of
a viral population in the face of
selection pressures

18. Evolution has 4 main
drivers:
Large number of progeny
Large number of mutants
Quasi-species effects
Selection

19. Evolution has 4 main
drivers:
Large number of
progeny
Large number of
mutants
Quasi-species effects
Selection
Large number of progeny

20. Evolution has 4 main
drivers:
Large number of
progeny
Large number of
mutants
Quasi-species effects
Selection
Large number of mutants
Diversity 
Successful
Viruses
DNA
DS
SS
RNA
SS
DS

21. A quasispecies is a well-defined distribution
of mutants that is generated by a mutation-
selection process.
Evolution has 4 main
drivers:
Large number of
progeny
Large number of
mutants
Quasi-species effects
Selection
Quasi-species effects

22. Evolution has 4 main
drivers:
Large number of
progeny
Large number of
mutants
Quasi-species effects
Selection
Selection
Survival of the fittest
Survival of the
survivors

23. Error
Threshold
Upper limit of mutation
rate

24. Genetic bottle neck
examples
How to avoid?

25. Recombinati
on

26. Selection: genetic Shift & Drift
Selection: In virulence a positive or negative trait

27. Evolution in 2012

28. Nice
idea


29. New viruses can only arise from viruses that are
already existed, not de novo

30. Constrains on virus evolution:
Viral genome is constrain
Physical nature of capsid
Extreme alteration in viral consensus
genome do not survive selection

31. REFERENCES
• 1. Virology principles and application, JHON CARTER AND
VENETIA SAUNDERS.
• 2. The origin and Evolution of Viruses, ESTEBAN DOMINGO AND
JOHN J. HOLLAND.
• 3.

32. Thanks for
listening
ANYQuestio
ns?