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Flip to reveal answersWhat does it mean that viruses are probably 'polyphyletic'?
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All 7 Flashcards — Origin and rapid evolution of viruses
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Question
What does it mean that viruses are probably 'polyphyletic'?
Answer
They have **multiple independent origins** — viruses probably arose **several separate times**, not from one common ancestor.
Question
Name the three hypotheses for the origin of viruses.
Answer
**Escape** (host genes/mobile elements gained a capsid), **reduction** (free-living parasitic cells lost genes), and **virus-first** (self-replicating molecules co-evolved with early cells).
Question
Why is the origin of viruses 'uncertain'?
Answer
Viruses are non-cellular and leave no fossils, and each hypothesis explains only **some** viruses — so there is **no single agreed origin**.
Question
Why do viruses evolve so rapidly?
Answer
**Huge populations + very short generation times + high mutation rates** mean **natural selection** acts on them extremely fast.
Question
Why do RNA viruses mutate especially fast?
Answer
Their **polymerases lack proofreading**, so many copying errors (mutations) accumulate each generation.
Question
Antigenic drift vs antigenic shift?
Answer
**Drift** = small, gradual mutations in the surface proteins. **Shift** = a large, sudden change when two strains **swap whole genome segments**.
Question
Why must flu and COVID vaccines be updated?
Answer
Variants with **changed surface proteins** escape existing immunity and are **selected for**, so the circulating strain no longer matches the old vaccine.
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Viruses
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