Other ways populations change: drift, gene flow and mutation

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   A meadow before and after a model flood (model data)

   when	plants	alleles	R alleles
   before the flood	1,000	2,000	1,200
   after the flood	20	40	14

2. 1.

   A model flood that favored no allele left 20 plants. Ari wants p, the frequency of R, in the plants that remained. What is it?

   • 0.7: 14 R alleles out of 20 plants
   • 14: the number of R alleles that remain
   • 0.35: 14 of the 40 alleles are R
   • 0.6: the flood leaves p unchanged

3. A mainland meadow and four founding seeds (model data)

   group	seeds or plants	alleles	R alleles
   mainland meadow	500	1,000	700
   four founding seeds	4	8	2

4. 2.

   Bo compares a mainland meadow with an island population started from 4 seeds. Each seed holds 2 alleles. What is p for R on the island at the start?

   • 0.7: the founders match the mainland meadow
   • 0.25: 2 of the 8 founding alleles are R
   • 2: the number of R alleles among the founders
   • 0.5: 2 of the 4 seeds carry R

5. Allele R in two meadows before and after wind carries seeds into meadow 2 (model data)

   group	alleles	R alleles	p for R
   meadow 1	500	400	0.8
   meadow 2 before the seeds	300	60	0.2
   seeds carried into meadow 2	100	80	0.8

6. 3.

   Wind carries seeds from meadow 1 into meadow 2, and the seedlings join it. Jun recomputes p for R in meadow 2. Which statement is correct?

   • 0.35, so meadow 2 is now closer to meadow 1 than before
   • 0.15, as 60 R alleles shared among the 400 alleles
   • 0.35, so meadow 2 is now farther from meadow 1 than before
   • 0.5, the average of 0.8 and 0.2 with the sizes ignored

7. R alleles in two populations when no allele helps survival (model data)

   generation	10 plants (20 alleles): R alleles	1,000 plants (2,000 alleles): R alleles
   0	10	1,000
   1	12	1,010
   2	15	1,017
   3	17	996
   4	15	990

8. 4.

   Kira compares how far p, the frequency of R, moved from generation 0 to generation 4 in each population. Which pair is correct?

   • 10 plants: 0.25; 1,000 plants: 0.25
   • 10 plants: 0.005; 1,000 plants: 0.25
   • 10 plants: 0.25; 1,000 plants: 0.005
   • 10 plants: 5; 1,000 plants: 10

9. R alleles at generation 10 in six runs of each size (model data)

   run	10 plants (20 alleles): R alleles	1,000 plants (2,000 alleles): R alleles
   1	0	1,024
   2	11	1,069
   3	15	988
   4	6	913
   5	20	991
   6	13	1,014

10. 5.

    Luz compares six runs of each size, all started at half R alleles. No allele helps survival. Which statement about p fits the table?

    • In the small runs p ranged from 0 to 1, while in the large runs p stayed between 0.45 and 0.54
    • p ranged more in the large runs, since their R counts spread from 913 to 1,069
    • In the small runs p stayed near 0.50, since chance cancels out in small groups
    • p rose in the 12 runs, since R was the better allele

11. Four small populations that each started with 10 of 20 alleles being R (model data)

    population	R plants that survive to breed	W plants that survive to breed	R alleles of 20 after generation 6
    1	60%	60%	20
    2	60%	60%	0
    3	60%	60%	13
    4	60%	60%	4

12. 6.

    Noah sees four populations start the same and end in different places. R and W plants survive to breed at the same rate. What best explains the end points?

    • Natural selection: R plants had a survival advantage in populations 1 and 3
    • Genetic drift: chance moved R up in some populations and down in others
    • Gene flow: alleles arriving from outside set each population's end point
    • Genetic drift: chance moved the four populations toward the better allele

13. A population of 5,000 plants where R plants survive to breed 90% of the time and W plants 60% (model data)

    generation	p for R
    0	0.50
    1	0.60
    2	0.69
    3	0.77
    4	0.84

14. 7.

    Pia sees p for R rise steadily in a large population of 5,000 plants. Which force best explains the steady rise?

    • Gene flow: R alleles arrived in seeds from outside the population
    • Genetic drift: chance pushed p upward each generation
    • Natural selection: R plants survive to breed more often
    • Mutation: new R alleles appeared in many plants each generation

15. A meadow before and after a model flood (model data)

    when	plants	R alleles	W alleles	Y alleles
    before the flood	1,000	1,000	800	200
    after the flood	6	7	5	0

16. 8.

    A model flood that favored no allele left 6 plants. Tala compares the meadow before and after. What does the table show about variation?

    • Allele Y was lost, so the survivors hold less variation than before
    • The three alleles remain, so the flood left the variation unchanged
    • Allele Y was lost because Y is a harmful allele
    • Allele W was lost, since W had fewer copies than R

17. Alleles in a mainland meadow and in four founding seeds (model data)

    group	R alleles	W alleles	Y alleles
    mainland meadow (1,000 alleles)	500	400	100
    four founding seeds (8 alleles)	5	3	0

18. 9.

    Wind carried four seeds from a mainland meadow to an empty island. Zee reads the table. Which statement about the new island population is correct?

    • It starts with only the alleles its founders carried, here R and W
    • It lacks Y because Y is harmful on islands, so island plants lack it
    • It starts as a small copy of the meadow, with Y in the same share
    • Y will soon reappear by mutation, since mutation is common each generation

19. A model mutation rate for one gene (model data)

    item	value
    copies of the gene in the population	2,000
    chance that one copy changes to allele V in one generation	1 in 100,000

20. 10.

    In this model, mutation can change a copy of a gene into a new allele V. Esme estimates the new V alleles per generation. What is it?

    • About 2, from 2,000 ÷ 1,000, so V appears in a few seeds
    • About 200, so mutation changes a tenth of the alleles each generation
    • About 0.02, so most generations add no V allele
    • About 20