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Evolution, species and phylogeny

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Which statement describes evolution most precisely?

  1. One animal exercises and becomes stronger.
  2. A small founding population on an island changes allele frequency only because of natural selection.
  3. A population's heritable composition changes over generations.
  4. Every organism chooses a useful allele.
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A population's heritable composition changes over generations.

This distinguishes population evolution from individual adjustment.

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Which statement is NOT part of the theory of evolution by natural selection?

  1. Better-adapted individuals leave more offspring
  2. Individuals in a population show heritable variation
  3. Organisms acquire needed traits and pass them on
  4. More offspring are produced than can survive
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Organisms acquire needed traits and pass them on

That is inheritance of acquired characteristics. Selection acts on heritable variation that already exists.

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Which diagram best represents descent with modification?

  1. A ladder with modern humans as the required final goal
  2. A branching tree with shared ancestors and diverging descendants
  3. A network joining species only by their current habitat
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A branching tree with shared ancestors and diverging descendants

Branching captures both shared inheritance and divergence.

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What does Wallace's biogeographical evidence emphasise?

  1. Current climate alone explains fauna, regardless of historical barriers.
  2. Distribution patterns can reflect ancestry, isolation and geological history.
  3. Every island has identical evolutionary history.
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Distribution patterns can reflect ancestry, isolation and geological history.

Geography supplies evidence independent of simple external resemblance.

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Why is the biological species concept hard to apply to fossils?

  1. Every fossil is necessarily a different species.
  2. Fossils show adaptive radiation, which proves that every fossil belongs to its own species.
  3. Their natural interbreeding and fertility cannot be directly tested.
  4. Fossils have no anatomical evidence.
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Their natural interbreeding and fertility cannot be directly tested.

Reproductive criteria are usually unavailable for extinct specimens.

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What is a phylogeny intended to show?

  1. Only the habitat of each organism today
  2. A sequence ranking lineages by increasing complexity
  3. Evolutionary relationships among lineages
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Evolutionary relationships among lineages

It represents a hypothesis of ancestry and divergence.

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Differences in a protein sequence: species W and X, 3; W and Y, 12; X and Y, 13; W and Z, 25. Which species are most closely related?

  1. W and X
  2. W and Z
  3. X and Y
  4. W and Y
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W and X

They differ at only 3 positions, the fewest, so they share the most recent common ancestor.

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Why compare multiple genes rather than one short sequence?

  1. To avoid aligning any sequences
  2. To guarantee every gene has an identical evolutionary history
  3. To make sure the mutation rate is the same in every gene.
  4. To use more independent characters and reduce dependence on an atypical region
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To use more independent characters and reduce dependence on an atypical region

Broader evidence can improve and test the inferred relationship.

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Write a short answer, then compare it with a sample and check for missing ideas.

Question 1 of 9

Build a tree and date the splits

4 marks

Invented differences in one 1,000-base gene: P and Q differ at 30 bases; P and R at 90; Q and R at 90; S differs from each of P, Q and R at 180. Fossils show that P and Q diverged 5 million years ago. (a) Describe the tree these data support. (b) Calculate the rate of change for the pair per year. (c) Estimate when R and S split from the others. (d) State the assumption behind (c) and one reason it may fail. [4]

Fewest differences join first. Rate = differences / time. Show units.

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