Other ways populations change: drift, gene flow and mutation

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   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

2. 1.

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

   • 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
   • Drift raised R in all six runs, since all six ended above 10

3. 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

4. 2.

   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?

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

5. Three runs of a 10-plant population (20 alleles) when no allele helps survival (model data)

   generation	run 1: R alleles	run 2: R alleles	run 3: R alleles
   0	10	10	10
   2	3	16	7
   4	0	20	6
   6	0	20	10

6. 3.

   Kira sees that three runs ended far apart, yet the end counts average to 10, the starting count. What explains this?

   • The table must have an error, since runs from one start should end alike
   • Selection raised R in one run and lowered it in another, keeping the average
   • Drift pulls each population back toward half R over time
   • Drift moved each run up or down by chance, so the changes cancel on average

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?

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

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

11. Notebook

    Notes on two model runs (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Population A has 10 plants and population B has 1,000 plants; no allele helps survival. Line 2: R fell from 10 to 0 of 20 alleles in A, and stayed near 1,000 of 2,000 in B. Line 3: So drift steadily removes the less useful allele from small populations. Line 4: Chance moves A more because one plant is a larger share of its gene pool.

12. 6.

    Pia reads a classmate's notebook about two model runs. Which line has the mistake?

    • Line 3: drift is chance, not a steady removal of the less useful allele
    • Line 4: one plant is the same share of both gene pools
    • Line 1: a model run needs the same number of plants in both populations to compare them
    • Line 2: R cannot fall to 0 when no allele helps survival

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 2: 100 alleles with 70 R alleles would give p = 0.07
    • Line 3: 100 R alleles among 400 alleles gives p = 0.4, so the stated 0.25 is a miscount
    • 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

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

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?

    • 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
    • Chance changes the small gene pool more, since one plant is a larger share of it
    • Both populations keep the same alleles, since a smaller group is a copy of a larger one

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?

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