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WELCOME
VIRUSES ORIGIN AND EVOLUTIONELHALABI HASANCHEBAT DIMASUPERVISION: DR. F. MONEM,
VIROLOGY
PhD
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?
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
WHERE DID VIRUSES COME FORM?
!THE MAIN QUESTION NEEDS TO BE ANWERED IS:
WHAT ARE VIRUSES?
• Parasites, selective infection.• Living or not?• Genetics:• RNA viruses• DNA viruses
• Structure:• Capsid• Genome
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?
TIME LINE OF EARTH HISTORY
THEORIES ON THE ORIGIN OF VIRUSES
• 1. Molecular precursors of cellular organisms• 2. Components of cells• 3. Intracellular micro-organisms.
1. MOLECULAR PRECURSORS OF CELLULAR ORGANISMS
• RNAs were originated before cells and had many features.• What happened as cells
evolved?
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?
2. COMPONENTS OF CELLS
• 5. Are we made of viruses?:• Chicken-and-egg situation
betweenretrotransposons and retroviruses!!• HGSP: 8% of genom is LTR-
flanked
3. INTRACELLULAR M.O.
• degeneracy of intracellular M.O. until the it becomes a virus?
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.
Evolution of viruses
Evolution is the constant change of a viral population in the face of selection pressures
Why?
Proliferate faster than
•New viral diseases•Regular bouts every day•Drug resistent
Evolution has 4 main drivers:
Large number of progenyLarge number of mutantsQuasi-species effectsSelection
Evolution has 4 main drivers:
Large number of progenyLarge number of mutantsQuasi-species effectsSelection
Large number of progeny
Evolution has 4 main drivers:
Large number of progenyLarge number of mutantsQuasi-species effectsSelection
Large number of mutantsDiversity Successful
Viruses
DNA
DS
SS
RNA
SS
DS
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 progenyLarge number of mutantsQuasi-species effectsSelection
Quasi-species effects
Evolution has 4 main drivers:
Large number of progenyLarge number of mutantsQuasi-species effectsSelection
SelectionSurvival of the fittestSurvival of the survivors
Error Threshold
Upper limit of mutation rate
Genetic bottle neck
examples
How to avoid?
Recombination
Selection: genetic Shift & Drift
Selection: In virulence a positive or negative trait?
Evolution in 2012
Nice idea
Assumption:New viruses can only arise from viruses that are already existed, not de novo
Constrains on virus evolution:Viral genome is constrainPhysical nature of capsidExtreme alteration in viral consensus genome do not survive selection
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.
Thanks for listening
ANYQuestions?