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10.3: Microevolution and the Genetics of Populations

Created by: CK-12

Lesson 10.3: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. The fossil record reflects macroevolution.

_____ 2. Population genetics is a combination of evolutionary theory and Darwinian genetics.

_____ 3. For a gene with two alleles, if the frequency of one allele is 0.65, the frequency of the other allele is 0.30.

_____ 4. Hardy-Weinberg equilibrium can exist only in populations undergoing normal natural selection.

_____ 5. A forest fire can result in a bottleneck effect.

_____ 6. Individuals with sickle-cell anemia have a high fitness because they are resistant to malaria.

_____ 7. Natural selection causes allele frequencies to change.

_____ 8. Microevolution occurs over a very long period of time within a population or species.

_____ 9. Mutation creates new genetic variation in a gene pool.

_____ 10. Hardy-Weinberg equilibrium can only occur in a very small population.

_____ 11. Inbreeding in certain populations, together with the founder effect, can result in rare phenotypes within the population.

_____ 12. Directional selection occurs when one of two extreme phenotypes is selected for.

_____ 13. Hardy-Weinberg equilibrium conditions rarely occur in real populations.

_____ 14. Emigration results in gene flow.

_____ 15. Disruptive selection occurs when phenotypes at both extremes of the phenotypic distribution are selected against.

Lesson 10.3: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Forces of Evolution

The conditions for Hardy-Weinberg equilibrium are unlikely to be met in real populations. The Hardy-Weinberg theorem also describes populations in which allele frequencies are not changing. By definition, such populations are not evolving. How does the theorem help us understand evolution in the real world?

From the theorem, we can infer factors that cause allele frequencies to change. These factors are the forces of evolution. There are four such forces: mutation, gene flow, genetic drift, and natural selection.

Mutation

Mutation creates new genetic variation in a gene pool. It is how all new alleles first arise. In sexually reproducing species, the mutations that matter for evolution are those that occur in gametes. Only these mutations can be passed to offspring. For any given gene, the chance of a mutation occurring in a given gamete is very low. Thus, mutations alone do not have much effect on allele frequencies. However, mutations provide the genetic variation needed for other forces of evolution to act.

Gene Flow

Gene flow occurs when people move into or out of a population. If the rate of migration is high, this can have a significant effect on allele frequencies. Both the population they leave and the population they enter may change.

During the Vietnam War in the 1960s and 1970s, many American servicemen had children with Vietnamese women. Most of the servicemen returned to the United States after the war. However, they left copies of their genes behind in their offspring. In this way, they changed the allele frequencies in the Vietnamese gene pool. Was the gene pool of the American population also affected? Why or why not?

Genetic Drift

Genetic drift is a random change in allele frequencies that occurs in a small population. When a small number of parents produce just a few offspring, allele frequencies in the offspring may differ, by chance, from allele frequencies in the parents. This is like tossing a coin. If you toss a coin just a few times, you may by chance get more or less than the expected 50 percent heads or tails. In a small population, you may also by chance get different allele frequencies than expected in the next generation. In this way, allele frequencies may drift over time. Genetic drift occurs under two special conditions. They are called bottleneck effect and founder effect.

  1. Bottleneck effect occurs when a population suddenly gets much smaller. This might happen because of a natural disaster, such as a forest fire. By chance, allele frequencies of the survivors may be different from those of the original population.
  2. Founder effect occurs when a few individuals start, or found, a new population. By chance, allele frequencies of the founders may be different from allele frequencies of the population they left.

Questions

1. What are the forces of evolution?

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2. Describe the type of mutations that affect evolution. Why?

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3. Was the gene pool of the American population also affected by the gene flow described above? Why or why not?

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4. What is genetic drift?

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5. Describe one special condition under which genetic drift occurs.

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Lesson 10.3: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. The main difference between macroevolution and microevolution is
    1. the time frame of the evolutionary process.
    2. the species that evolve during each.
    3. that microevolution is only for small organisms, and macroevolution is for large organisms.
    4. all of the above
  2. Which of the following statements is correct?
    1. Individuals do not evolve, genes do evolve.
    2. Individuals do not evolve, populations do evolve.
    3. Populations do not evolve, individuals do evolve.
    4. Populations do not evolve, species do evolve.
  3. Which of the following statements is true concerning mutations? (1) Mutations are how all new alleles first arise. (2) Mutations create new genetic variation in a gene pool. (3) Only mutations that occur in gametes influence evolution. (4) Mutations really do not have much influence on allele frequencies.
    1. 1 and 2
    2. 2 and 4
    3. 1, 2, and 3
    4. 1, 2, 3, and 4
  4. In a population with 100 members, the total number of copies of each gene in the population is
    1. 50.
    2. 100.
    3. 200.
    4. 400.
  5. In a population with 100 members, if there are 120 dominant alleles, how many recessive alleles are there?
    1. 60
    2. 80
    3. 120
    4. 240
  6. In a population with 100 members, if 9 individuals have the recessive phenotype, how many individuals are heterozygous?
    1. 9
    2. 21
    3. 42
    4. 70
  7. The forces of evolution include
    1. natural selection.
    2. gene drift.
    3. genetic flow.
    4. all of the above
  8. Which of the following describes disruptive selection?
    1. Selection that occurs when one of two extreme phenotypes is selected for.
    2. Selection that occurs when phenotypes at both extremes of the phenotypic distribution are selected against.
    3. Selection that occurs when phenotypes in the middle of the range are selected against.
    4. Selection that occurs when one phenotype is disrupted and goes extinct.

Lesson 10.3: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. consists of all the genes of all the members of the population

_____ 2. creates new genetic variation in a gene pool

_____ 3. occurs over geologic time above the level of the species

_____ 4. occurs when one of two extreme phenotypes is selected for

_____ 5. refers to differences between the phenotypes of males and females of the same species

_____ 6. occurs when phenotypes in the middle of the range are selected against

_____ 7. occurs when people move into or out of a population

_____ 8. occurs over a relatively short period of time within a population or species

_____ 9. occurs when phenotypes at both extremes of the phenotypic distribution are selected against

_____ 10. how often an allele occurs in a gene pool relative to the other alleles for that gene

_____ 11. the science that focuses on evolution within populations

_____ 12. shows that allele frequencies do not change in a population if certain conditions are met

Terms

a. allele frequency

b. directional selection

c. disruptive selection

d. gene flow

e. gene pool

f. Hardy-Weinberg theorem

g. macroevolution

h. microevolution

i. mutation

j. population genetics

k. sexual dimorphism

l. stabilizing selection

Lesson 10.3: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. ____________ occurs over a relatively short period of time within a population or species.

2. ____________ occurs over geologic time above the level of the species.

3. The ____________ theorem shows that allele frequencies do not change in a population if certain conditions are met.

4. Natural selection occurs when there are differences in ____________ among members of a population.

5. Genetic ____________ is a random change in allele frequencies that occurs in a small population.

6. The gene ____________ consists of all the genes of all the members of the population.

7. Mutation creates new ____________ variation in a gene pool.

8. Gene ____________ occurs when people move into or out of a population.

9. Allele ____________ is how often an allele occurs in a gene pool.

10. ____________ selection occurs when one of two extreme phenotypes is selected for.

11. ____________ selection occurs when phenotypes in the middle of the range are selected against.

12. Population ____________ focuses on evolution within populations.

Lesson 10.3: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Distinguish between microevolution and macroevolution.

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