Speciation: Isolation, Hybrid Zones and Where the Boundary Blurs · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When one group becomes two

Science · Genetics & Evolution · ages 19-21
Name ______________________   Date ____________

  1. Which barrier acts after mating and birth?

    • Different dances
    • Mismatched seasons
    • Sterile adult hybrids

  2. Which barrier acts before mating happens?

    • Season mismatch
    • Hybrid sterility
    • Hybrid failure

  3. Two groups meet in a thin steady mixed strip. What does it mean?

    • Walls are weak and genomes blend
    • Walls are strong and hold
    • Mating stopped entirely

  4. Mixed young keep failing. What does selection favour at the contact strip?

    • It labels rocks
    • It waters plants
    • It sharpens early blocks where groups meet

  5. Why must long gone groups be judged from shape and rock layers?

    • Crossing is impossible, so form and time judge it
    • It crosses easily in labs
    • It breeds with living cousins

  6. A river splits one group in two. What kind of split starts?

    • Splitting side by side with no map gap
    • Splitting across a map barrier
    • Merging back into one pool

  7. A friend applies the crossing test to solo breeders. Is that right?

    • Yes, crossing tests judge everything
    • No, they never cross to test
    • Yes, rocks can mate in labs

  8. Two meeting groups blend freely with thriving mixed young. Predict the outcome.

    • The split collapses back to one pool
    • The split completes at once
    • A new river appears
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Answer key

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

When one group becomes two W1-mt_ngZxpFlwo1-s1

  1. Sterile adult hybrids · A living but childless adult is a barrier that lands after joining.
  2. Season mismatch · Different seasons stop mating itself, while the others strike after joining.
  3. Walls are strong and hold · A thin steady strip means removal balances arrival, so the split holds.
  4. It sharpens early blocks where groups meet · Failed mixed young make early avoidance pay, so early walls grow taller.
  5. Crossing is impossible, so form and time judge it · Gone groups cannot mate, so workers delimit them from form and time.
  6. Splitting across a map barrier · Map gaps start the classic geographic split, while side by side splits need other walls.
  7. No, they never cross to test · The crossing rule needs mates and living groups, so keep several rules ready.
  8. The split collapses back to one pool · Healthy blending erases the divide, so the two pools merge again.
Worksheet · LightMySky