Annotation, orthologues and comparative genomics · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Gene relationships and functional hypotheses

Science · Genetics & Evolution · ages 21-22
Name ______________________   Date ____________

  1. A gene duplication produced two copies that remain in one genome. What is their relationship?

    • Orthologues from speciation
    • Paralogues from duplication
    • Unrelated genes with no shared ancestor

  2. A human gene and a mouse gene descend from copies separated by the human-mouse speciation event, with no intervening duplication. What is their relationship?

    • Orthologues from speciation
    • Paralogues from duplication
    • Alleles at one present-day locus

  3. Sequence similarity alone confirms that a newly annotated gene performs the proposed function.

    Circle one:   True   False

  4. A region changes much less across distant species than a suitable neutral model predicts. What does this support?

    • Purifying selection may constrain the region
    • The region must be the fastest-mutating part of each genome
    • The comparison proves its exact regulatory target without tests

  5. How should orthology and paralogy inform a prediction about gene function?

    • Assume every paralogue has lost all ancestral activity
    • Assume every orthologue has identical activity and expression
    • Use ancestry with activity and expression evidence

  6. What limits an inference based on unchanged sequence alone?

    • Conserved DNA cannot perform any structural or regulatory function
    • Sequence identity always reveals the exact biochemical activity
    • A low mutation rate can preserve sequence without revealing its role

  7. A new gene is an orthologue of a studied enzyme, but its tissue expression differs. How should the detailed function be transferred?

    • Keep the function provisional and test it in context
    • Transfer every functional detail because orthologues cannot diverge
    • Reject shared activity because expression proves a different reaction

  8. A non-coding region is strongly conserved across distant species. Which next step tests a possible regulatory role?

    • Assign the nearest gene as its target without testing
    • Change the region and measure gene expression
    • Discard the region because it does not encode a protein
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Answer key

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Gene relationships and functional hypotheses W1-mt_eBRge2bLeC-s1

  1. Paralogues from duplication · The copies share ancestry through duplication, so they are paralogues.
  2. Orthologues from speciation · Speciation is the ancestral event separating the copies, which defines orthology.
  3. False · Similarity supports a prediction. Confirmation needs evidence about the proposed activity in context.
  4. Purifying selection may constrain the region · Reduced change relative to the neutral expectation can support selection against harmful changes, without identifying an exact function.
  5. Use ancestry with activity and expression evidence · Ancestry guides predictions, while activity, expression and regulation can change in either relationship.
  6. A low mutation rate can preserve sequence without revealing its role · A neutral expectation is needed to interpret little change. Even evidence of constraint does not identify an exact role.
  7. Keep the function provisional and test it in context · Orthology supports investigation. Differing expression cautions against copying every detail but does not rule out shared activity.
  8. Change the region and measure gene expression · Changing the region and comparing expression with suitable samples tests a regulatory hypothesis. Conservation alone identifies no target.
Worksheet · LightMySky