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 grew because seedlings add differences
   • 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

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?

   • 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
   • Selection failed in runs 3, 5 and 6, since R did not reach 20

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?

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

7. 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

8. 4.

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

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

9. 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

10. 5.

    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?

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

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 1: a meadow of 1,000 plants cannot hold three alleles
    • Line 3: a small sample can lose alleles and change their shares
    • 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 4: gene flow made the meadows more alike, as the gap fell from 0.6 to 0.45
    • 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

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 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
    • The island differs, since mutation changed R to W on the way
    • The island matches the mainland, since the founders are a small copy of the whole meadow

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 small gene pool more, since one plant is a larger share of it
    • Chance moves both gene pools toward the better allele, since the weaker plant is lost
    • Chance changes the large gene pool more, since it has more plants to lose
    • 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
    • Genetic drift made Y in meadow 2, since chance creates new alleles
    • 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