Selection on Quantitative Traits and Predicting the Response · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Pick the parents, predict the herd

Science · Genetics & Evolution · ages 19-20
Name ______________________   Date ____________

  1. The pick gap is 10 units and the inherited share is 0.5. What is the response?

    Answer: ______________

  2. What rule predicts the next generation average?

    • Response times pressure squared
    • Response equals inherited share times the pick gap
    • Response ignores inheritance

  3. Breeders keep only the tallest each round. What happens to middle and spread?

    • Middle moves, spread steady
    • Middle steady, spread shrinks
    • Middle steady, spread grows

  4. You compute the pick gap. Which average do you subtract?

    • The picked parents average
    • The next generation average
    • The whole herd average

  5. Removing both extremes each round narrows the spread without moving the middle.

    Circle one:   True   False

  6. A big push targets a barely passed trait. What do you predict?

    • The herd moves only slightly
    • The herd leaps forward
    • The herd splits in two

  7. A friend says one sided picking keeps the middle fixed. Is that right?

    • Yes, pushing never moves anything
    • Yes, only trimming moves the middle
    • No, pushing one side drags the middle along

  8. After many top pick rounds each gain shrinks. Why did the response stall?

    • Fresh variation appears
    • Usable variation ran out and costs bite
    • The rule broke down
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Answer key

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

Pick the parents, predict the herd W1-mt_M-czTLDmfl-s1

  1. 5 · Half of a ten unit pick gap passes on, so the herd moves five units.
  2. Response equals inherited share times the pick gap · Multiply the pick gap by the inherited share to get the next step.
  3. Middle moves, spread steady · Pushing one side drags the middle along while the width holds.
  4. The whole herd average · Subtract the herd average from the picked average to find the push.
  5. True · Trimming both ends each round favours the middle and squeezes variance.
  6. The herd moves only slightly · Only the passed fraction of an edge reaches the next round.
  7. No, pushing one side drags the middle along · A shifting middle with steady width is the signature of one sided pressure.
  8. Usable variation ran out and costs bite · Shrinking variation plus opposing pressures cancel further gains.
Worksheet · LightMySky