2017/2018- Essay 1 Flashcards
What are the 3 theories
Intro- Paragraph 1
Discuss the 3 main hypotheses as to the evolutionary origin of viruses. Indicate for each hypothesis where viruses fit phylogenetically
- Evolutionary origin- ongoing debate
- 3 main hypothesis how viruses arose
- regressive hypothesis
- Cellular origin hypothesis
- Coevolution hypothesis
Explain regressive hypothesis
Paragraph 2
*Discuss** the 3 main hypotheses as to the evolutionary origin of viruses. Indicate for each hypothesis where viruses fit phylogenetically
-Regressive hypothesis
- Virus evolved fromfree-living cells that lost many of their genes over time
- Eventually dependent on host cell for survival
- Hypothesis suggesys- virus may be degenerate forms of bacteria/other microorganisms
- Hypothesis difficult to test - why? > no known intermediates between free-livng and viruses
- Would be located on of the branches leading to prokaryotes/ eukaryotes
Explain cellular origin hypothesis
Paragraph 3
*Discuss** the 3 main hypotheses as to the evolutionary origin of viruses. Indicate for each hypothesis where viruses fit phylogenetically
Cellular origin hypothesis
- viruses evolved from genetic elements
- that can move between cells (transposons/plasmids)
- Suggest- ancient genetic elements that becamse encapsulated in protein coats - allows them to infect cell
- as they are closely related to the genetic elements that evolved from
- located: branch leading to prokaryotes/ eukaryotes
Explain coevolution hypothesis
Paragraph 4
*Discuss** the 3 main hypotheses as to the evolutionary origin of viruses. Indicate for each hypothesis where viruses fit phylogenetically
-Coevolved from a common ancestor
-with viruses evolving alonside cells as a separate liineage
-suggest: virus have always been distinct from cells and have adapted to infect specific hosts over time
-suggest: separate evolutionary history from cells
-Phylogenetic tree: located- located on a brance that diverged early in the evolution of life
