Sequencing Reads and How a Genome Is Assembled · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Rebuilding a genome from short reads

Science · Genetics & Evolution · ages 20-22
Name ______________________   Date ____________

  1. How is a genome rebuilt from reads?

    • By finding overlaps and joining them
    • By sorting reads by length
    • By counting the machines used

  2. What comes out of a sequencing instrument?

    • One finished genome
    • Many short reads
    • A printed chromosome map

  3. What does more coverage do to base accuracy?

    • It lowers it
    • It leaves it unchanged
    • It improves it

  4. You need cheap accurate bases over simple ground. Which reads do you pick?

    • Short reads
    • No reads at all
    • Reads from another species

  5. The same 1,000-base stretch appears in five places. A 150-base read lands inside one copy. What is the problem?

    • The read fits all five copies, so its home is ambiguous
    • The read is too long to use
    • The copies delete themselves

  6. A long read can resolve a repeat by spanning it and anchoring both sides.

    Circle one:   True   False

  7. Unique regions assemble easily because each read has only one plausible home.

    Circle one:   True   False

  8. A team doubles coverage to fix a tangled repeat, but the tangle stays. What is wrong?

    • They sequenced too little DNA
    • Coverage sharpens bases but short reads still cannot span the repeat
    • Repeats vanish at high coverage
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Rebuilding a genome from short reads W1-mt_4mUJIUAZGd-s1

  1. By finding overlaps and joining them · Overlapping ends reveal how snippets connect.
  2. Many short reads · The machine yields snippets that must be joined later.
  3. It improves it · Extra reads outvote random errors at each position.
  4. Short reads · Short reads give accurate bases at low cost where repeats are absent.
  5. The read fits all five copies, so its home is ambiguous · Short reads cannot anchor a repeat that exceeds their length.
  6. True · Unique flanks on both sides reveal which copy it is.
  7. True · Ambiguity is the hard part, and unique ground avoids it.
  8. Coverage sharpens bases but short reads still cannot span the repeat · Accuracy is not the block; read length is, so longer reads are needed.
Worksheet · LightMySky