Other ways populations change: drift, gene flow and mutation

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   A meadow after a model flood, then after seeds arrive from the source meadow (model data)

   group	alleles	R alleles	p for R
   source meadow	2,000	1,000	0.5
   survivors of the flood	40	8	0.2
   seeds arriving from the source meadow	60	30	0.5

2. 1.

   After a model flood, seedlings from the source meadow join the survivors. Ari recomputes p for R. What is the new p, and what happened to the gap from the source meadow's p?

   • 0.50, and the gap to the source meadow closed completely to 0
   • 0.38, and the gap to the source meadow shrank from 0.30 to 0.12
   • 0.35, the average of 0.2 and 0.5, with the gap shrinking to 0.15
   • 0.38, and the gap to the source meadow grew because seedlings add differences

3. Six runs of a 10-plant population (20 alleles) where R plants survive to breed 70% of the time and W plants 50% (model data)

   run	R alleles of 20 at generation 8
   1	19
   2	20
   3	11
   4	20
   5	12
   6	11

4. 2.

   Bo reads six model runs that began with 10 of 20 alleles being R. Which statement fits the table?

   • Drift raised R in all six runs, since all six ended above 10
   • Selection failed in runs 3, 5 and 6, since R did not reach 20
   • Selection raised R in all six runs, and drift made the end counts differ
   • Drift scattered the end counts, and a larger population would scatter them more

5. A source meadow and two islands, each started by 5 seeds (model data)

   place	alleles	R alleles	p for R
   source meadow	2,000	1,000	0.5
   island 1	200	140	0.7
   island 2	200	40	0.2

6. 3.

   Each island began with 5 seeds from one meadow. Wind later carries seeds between the islands until they form one population. Jun recomputes p for R in it. What is it?

   • 0.45: 180 of the 400 alleles are R, closer to the source's 0.5
   • 0.90: the sum of the p values of the two islands, 0.7 and 0.2
   • 0.18: 180 R alleles shared among the 1,000 alleles of the source meadow
   • 0.50: islands founded from one meadow have the same p as that meadow

7. A meadow before and after a model flood that favored no allele (model data)

   when	plants	alleles	R alleles	p for R
   before the flood	1,000	2,000	800	0.40
   after the flood	10	20	13	0.65

8. 4.

   R and W plants were equally likely to remain after a model flood. Luz sees p for R rise from 0.40 to 0.65. Why did p change?

   • The 10 remaining plants were a chance sample, so p can differ from the original
   • A sample of 10 plants should match the original p, so the table must have an error
   • R mutated more often during the flood, which raised p to 0.65
   • R plants were better at surviving the flood, so p rose

9. Use the table

   Allele V in a population of 1,000 plants (2,000 alleles) when each V plant leaves 1.5 times as many surviving young (model data)

   generation	V alleles of 2,000
   0	1
   10	56
   20	1,249
   30	1,979

10. 5.

    Mutation made allele V once, in generation 0. Milo sees V grow from 1 copy to 1,979. Mutation is rare, so what explains the growth?

    • Drift pushed V upward each generation until V was common
    • Mutation made new V alleles in many plants each generation, so the share of V kept growing
    • V plants left more surviving young, so selection raised V after the one mutation
    • Gene flow brought V in from other populations over time

11. Notebook

    Notes on a model flood (classmate's notebook), 4 lines. Columns: line, entry. Line 1: A meadow of 1,000 plants held alleles R, W and Y; a model flood left 8 plants. Line 2: The flood favored no allele, so the 8 plants were a chance sample. Line 3: So the 8 plants must still hold all three alleles in the same shares. Line 4: Regrowth adds plants but not the alleles the 8 plants did not carry.

12. 6.

    Ren reads a classmate's notebook about a model flood. Which line has the mistake?

    • Line 3: a small sample can lose alleles and change their shares
    • Line 1: a meadow of 1,000 plants cannot hold three alleles
    • Line 2: a flood that favors no allele cannot leave a chance sample
    • Line 4: a population that regrows regains the alleles it lost

13. Notebook

    Notes on two meadows and wind-carried seeds (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Meadow 1 had p = 0.7 for R with 500 alleles; meadow 2 had p = 0.1 with 300 alleles. Line 2: Wind carried seeds with 100 alleles, 70 of them R, from meadow 1 into meadow 2. Line 3: After the seedlings joined, meadow 2 had 100 R among 400 alleles, so p = 0.25. Line 4: So gene flow made the meadows more different, since meadow 2 changed.

14. 7.

    Tala reads a classmate's notebook about two meadows and wind-carried seeds. Which line has the mistake?

    • Line 1: 300 alleles at p = 0.1 hold 3 R alleles, not 30
    • Line 4: gene flow made the meadows more alike, as the gap fell from 0.6 to 0.45
    • Line 3: 100 R alleles among 400 alleles gives p = 0.4, so the stated 0.25 is a miscount
    • Line 2: 100 alleles with 70 R alleles would give p = 0.07

15. A mainland meadow and a new island population started by 4 seeds (model data)

    place	alleles	R alleles	p for R
    mainland meadow	1,000	600	0.6
    island founders	8	2	0.25

16. 8.

    Zee reads the table. Which claim and reason fit it?

    • The island matches the mainland, since the founders are a small copy of the whole meadow
    • The island differs, since mutation changed R to W on the way
    • The island differs, since the island favors W over R in each seed
    • The island differs from the mainland, since 4 founders were a small chance sample

17. One plant leaves no seedlings in two populations (model data)

    population	plants	alleles	alleles from that plant	share of the gene pool
    small	10	20	2	0.1
    large	1,000	2,000	2	0.001

18. 9.

    Esme reads the table. Which claim and reason fit it?

    • Both populations keep the same alleles, since a smaller group is a copy of a larger one
    • Chance changes the small gene pool more, since one plant is a larger share of it
    • Chance changes the large gene pool more, since it has more plants to lose
    • Chance moves both gene pools toward the better allele, since the weaker plant is lost

19. Alleles found in two meadows before and after seeds from meadow 1 arrive in meadow 2 (model data)

    meadow	before the seeds arrive	after the seeds arrive
    meadow 1	R, W, Y	R, W, Y
    meadow 2	R, W	R, W, Y

20. 10.

    Noah sees allele Y appear in meadow 2 after wind carries in seeds from meadow 1. Which claim and reason fit the table?

    • Gene flow brought Y and made the meadows more alike, since Y is now in both
    • Genetic drift made Y in meadow 2, since chance creates new alleles
    • Mutation made Y in meadow 2, since mutation is common in each generation
    • Gene flow brought Y and made the meadows less alike, since new alleles add differences