Other ways populations change: drift, gene flow and mutation
Grade 9 Science Worksheet
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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 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?
- 0.5: 2 of the 4 seeds carry R
- 2: the number of R alleles among the founders
- 0.25: 2 of the 8 founding alleles are R
- 0.7: the founders match the mainland meadow
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 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?
- 0.15, 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
- 0.35, so meadow 2 is now closer to meadow 1 than before
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 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: 5; 1,000 plants: 10
- 10 plants: 0.25; 1,000 plants: 0.005
- 10 plants: 0.005; 1,000 plants: 0.25
- 10 plants: 0.25; 1,000 plants: 0.25
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 Luz compares six runs of each size, all started at half R alleles. No allele helps survival. Which statement about p fits the table?
- p rose in the 12 runs, since R was the better allele
- In the small runs p stayed near 0.50, since chance cancels out in small groups
- p ranged more in the large runs, since their R counts spread from 913 to 1,069
- In the small runs p ranged from 0 to 1, while in the large runs p stayed between 0.45 and 0.54
Two pairs of meadows after 5 generations (meadow 1 began at p = 0.8 and meadow 2 at p = 0.3, in both pairs) (model data)
pair seeds carried between meadows p for R in meadow 1 p for R in meadow 2 pair X yes, by wind 0.57 0.53 pair Y no 0.81 0.29 Milo compares two pairs of meadows. In one pair, wind carries seeds between the meadows. What does the table show about gene flow?
- Gene flow lowered p in both meadows, since the pair with seeds ended lower
- Gene flow made the meadows more alike: p differs by 0.04 with seeds and 0.52 without
- Gene flow made no difference, since both pairs ended with the same gap
- Gene flow made the meadows more different: p differs by 0.52 with seeds and 0.04 without
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 Pia sees p for R rise steadily in a large population of 5,000 plants. Which force best explains the steady rise?
- Genetic drift: chance pushed p upward each generation
- Mutation: new R alleles appeared in many plants each generation
- Natural selection: R plants survive to breed more often
- Gene flow: R alleles arrived in seeds from outside the population
Four populations over one generation (model data)
case alleles R plants that survive W plants that survive p for R before p for R after 1 16 50% 50% 0.50 0.25 2 6,000 90% 40% 0.50 0.69 3 6,000 50% 50% 0.50 0.50 4 24 85% 30% 0.50 0.75 Ren compares four populations over one generation. Which case is best explained by genetic drift?
- Case 1: few alleles, equal survival, and p moved a lot
- Case 3: many alleles, equal survival, and p stayed the same
- Case 4: few alleles, and p rose where R plants survive more
- Case 2: many alleles, and p rose where R plants survive more
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 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 W was lost, since W had fewer copies than R
- The three alleles remain, so the flood left the variation unchanged
- Allele Y was lost, so the survivors hold less variation than before
- Allele Y was lost because Y is a harmful allele
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 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 as a small copy of the meadow, with Y in the same share
- 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
- Y will soon reappear by mutation, since mutation is common each generation
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 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 20
- 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