Gene Mutations and Their Consequences · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why some mutations wreck proteins

Science · Genetics & Evolution · ages 17-18
Name ______________________   Date ____________

  1. What is a frameshift mutation?

    • An insertion or deletion that slips the reading frame
    • A single base swapped with no frame effect
    • A stop codon repaired back into a sense codon

  2. What is a substitution mutation?

    • A base added into the sequence
    • A base removed from the sequence
    • One base swapped for another

  3. Every substitution changes the protein that the gene makes.

    Circle one:   True   False

  4. A codon change swaps one amino acid for another. Which type is this?

    • Missense
    • Silent
    • Frameshift

  5. Why is a substitution often mild in effect?

    • It rewrites the whole chromosome at once
    • It changes one codon only
    • It always creates an early stop

  6. A deletion removes exactly three bases. What is the likely result?

    • The frame slips and everything downstream garbles
    • One amino acid drops out but the frame holds
    • The whole gene is erased from the chromosome

  7. A student says every mutation is a disaster for the organism. What is the best reply?

    • Silent changes pass unnoticed and rare ones even help
    • Mutagens protect DNA from all copying errors
    • Frameshifts always repair themselves within a day

  8. One deleted base garbles most of the protein. Why is the damage so large?

    • The chromosome snaps into two pieces
    • Every codon after the deletion is misread
    • The cell immediately deletes the whole gene
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Answer key

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

Why some mutations wreck proteins W1-mt_CDcaL6-iVp-s1

  1. An insertion or deletion that slips the reading frame · When the lost or gained bases are not a multiple of three, every codon after shifts.
  2. One base swapped for another · Substitution swaps a single base. Adding is insertion and removing is deletion.
  3. False · Silent substitutions swap in a codon for the same amino acid, so the protein is unchanged.
  4. Missense · Missense means a different amino acid. Silent keeps the same one and frameshift scrambles many.
  5. It changes one codon only · One altered codon leaves the rest of the protein exactly as before.
  6. One amino acid drops out but the frame holds · Three is a full codon, so the frame survives with one amino acid missing.
  7. Silent changes pass unnoticed and rare ones even help · Many changes are neutral, and a lucky few open new options that spread.
  8. Every codon after the deletion is misread · One missing base is not a multiple of three, so the frame slips for the rest of the message.
Worksheet · LightMySky