Download Worksheet 17.2: Evolution as Genetic Change

Biology Honors I!
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Name _________________ Period ___
Worksheet 17.2: Evolution as Genetic Change in Populations
(pages 487-492; iBooks pages 829-838)
1. If a trait made an organism less likely to survive and reproduce, what would happen to
the allele for that trait?
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2. If a trait had no effect on an organism’s fitness, what would likely happen to the allele for
that trait?
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Use the table showing the evolution of a population of mice to answer Questions 3–5.
Initial Population
Generation 10
Generation 20
Generation 30
90%
Black
80%
Black
70% Black
40% Black
10% Brown
20% Brown
30% Brown
60% Brown
3. Is the trait for fur color a single-gene trait or a polygenic trait? Explain your answer.
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4. Describe how the relative frequency of fur color alleles is changing in this population
and propose one explanation for this change.
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Biology Honors I!
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5. Suppose a mutation causes a white fur phenotype to emerge in the population. What
might happen to the mouse population after 40 generations?
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6. What effect does stabilizing selection have on variation in a population?
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For Questions 7–9, match the type of selection with the correct situation.
Type of Selection
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7. Directional
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8. Stabilizing
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9. Disruptive
Situation
A. Individuals at the upper and lower ends of the curve have higher
fitness than individuals near the middle.
B. Individuals at one end of the curve have higher fitness than
individuals in the middle or at the other end.
C. Individuals near the center of the curve have higher fitness than
individuals at either end.
10. Draw the missing line in the graph on the right to show how disruptive selection affects
beak size.
For Questions 11–13, complete each statement by writing the correct word or words.
11. In small populations, random changes in !
is called genetic drift.
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Biology Honors I!
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Name _________________ Period ___
12. A situation in which allele frequencies change as a result of the migration of a small
subgroup of a population is known as the !
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13. The !
is a change in allele frequency following a
dramatic reduction in the size of a population.
14. In most populations, a trait that has higher fitness leads to greater numbers of
organisms with that trait. On the graphs below, dotted lines show the original population.
The solid lines show the population after selection has taken place.
Follow the directions:!
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Label the graph that shows stabilizing selection.
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Label the graph that shows disruptive selection.
original
population
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Number of Birds in Population
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Percentage of Human
Population
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original
population
Beak Size
Birth Weight
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Answer the questions.
15. With which type of selection do organisms in the middle of the curve have the highest
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fitness? !
16. In disruptive selection, organisms on which part of the curve have the lowest fitness?
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Biology Honors I!
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Name _________________ Period ___
17. How does the curve change in stabilizing selection?
A. The curve becomes shorter and wider.
B. The curve becomes taller and narrower.
C. The curve moves to the right.
18. The plants in an area have either very small or very large seeds. Birds with small
beaks can eat small seeds, and birds with large beaks can eat large seeds. Birds
with smaller beaks and birds with larger beaks become more common than birds
with medium beaks. What type of selection is this?
A. stabilizing selection
B. disruptive selection
C. directional selection
The Hardy-Weinberg Principle Genetic equilibrium occurs when the allele frequencies in a
population remain the same. If the allele frequencies do not change, the population will not
evolve. The Hardy-Weinberg principle lists the five conditions in which evolution does not
occur in a population.
19. Read the chart below. Use phrases in the word box to identify each condition that leads
to genetic equilibrium. The first row has been completed for you.
large population
random mating
no natural selection
no mutations
no movement
The Hardy-Weinberg Principle
large population
The more individuals in the population, the smaller
the effect of genetic drift.
No changes to genes means new alleles are not
introduced into the population’s gene pool.
Each individual in a population has the same chance
of passing on its alleles.
No new alleles are introduced into the population’s
gene pool by new individuals.
No phenotype can have a selective advantage over
another—all individuals have equal fitness.
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Biology Honors I!
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Read the descriptions below. Use what you know about the Hardy-Weinberg principle to
identify what is happening.
20. Genetic drift strongly affects the population.
A. small population
B. random mating
C. no movement into or out of the population
D. no natural selection
21. Lions with a darker fur color have the same chance to reproduce as lions with a lighter
fur color.
A. large population!
C. random mating
B. no mutations!
D. no natural selection
22. Fitness is basically the same among individuals in the population.
A. large population!
C. random mating
B. no mutations!
D. no natural selection
23. Complete the concept map about Genetic Drift
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