Download Document

17.1 Genes and Variation
Lesson Objectives
Define evolution in genetic terms.
Identify the main sources of genetic variation in a population.
State what determines the number of phenotypes for a trait.
Genetics Joins Evolutionary Theory
For Questions 1–4, complete each statement by writing the correct word or words.
1. Natural selection works on an organism’s
rather than its
.
2. A(n)
consists of all the genes, including the alleles for each gene, that are
present in a population.
3. A gene pool typically contains different
for each heritable trait.
4. The number of times that an allele occurs in a gene pool compared with the number of
times other alleles for the same gene occur is called the
of the population.
Use the circle graph of a sample mouse population to answer Questions 5–8.
5. THINK VISUALLY In the diagram below, use circles to represent the alleles within
each segment of the population. Draw the B alleles as solid circles and the b alleles as
outline circles. The total number of individuals in this population is
; the
total number of alleles is
.
6. How many alleles for black fur are in the sample population and what percentage of allele
frequency does that represent?
7. How many alleles for brown fur are in the sample population and what percentage of
allele frequency does that represent?
8. Describe how a geneticist might be able to tell that this population is evolving.
9. Can you determine whether an allele is dominant or recessive on the basis of the ratio of
phenotypes in the population? Explain your answer.
Sources of Genetic Variation
10. What are mutations? When do they affect evolution?
11. How does sexual reproduction affect a population’s genetic variation?
12. Identify two ways in which genes can be recombined during meiosis.
13. What is lateral gene transfer? How does it affect variation?
Single Gene and Polygenic Traits
14. Label the two graphs to show which represents a single-gene trait and which represents a
polygenic trait.
For Questions 15–19, write True if the statement is true. If the statement is false, change
the underlined word or words to make the statement true.
15. The number of phenotypes produced for a given trait depends on how
many genes control the trait.
16. Height in humans is an example of a single-gene trait.
17. Each gene of a polygenic trait often has two or more phenotypes.
18. A single polygenic trait often has many possible genotypes.
19. A symmetrical bell-shaped graph is typical of polygenic traits.
20. Use the Venn diagram to compare and contrast single-gene traits and polygenic traits.
Single-Gene Traits
Polygenic Traits
Both
Apply the Big idea
21. Why is genetic variation important to the process of evolution?
17.2 Evolution as Genetic Change in
Populations
Lesson Objectives
Explain how natural selection affects single-gene and polygenic traits.
Describe genetic drift.
Explain how different factors affect genetic equilibrium.
How Natural Selection Works
1. If a trait made an organism less likely to survive and reproduce, what would happen to
the allele for that trait?
2. If a trait had no effect on an organism’s fitness, what would likely happen to the allele for
that trait?
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%
80%
70%
40%
10%
20%
30%
60%
3. Is the trait for fur color a single-gene trait or a polygenic trait? Explain your answer.
4. Describe how the relative frequency of fur color alleles is changing in this population and
propose one explanation for this change.
5. Suppose a mutation causes a white fur phenotype to emerge in the population. What
might happen to the mouse population after 40 generations?
6. What effect does stabilizing selection have on variation in a population?
For Questions 7–9, match the type of selection with the correct situation.
Type of Selection
7. Directional
8. Stabilizing
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 to
the right to show how disruptive
selection affects beak size.
Genetic Drift
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.
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
.
13. The
is a change in allele frequency following a dramatic
reduction in the size of a population.
14. Complete the concept map.
Genetic Drift
can result from
Bottleneck Effect
caused by
caused by
Evolution Versus Genetic Equilibrium
15. What does the Hardy-Weinberg principle state?
16. What is genetic equilibrium?
17. List the five conditions that can disturb genetic equilibrium and cause evolution to occur.
18. Explain how sexual selection results in non-random mating.
19. Suppose a population of insects live in a sandy habitat. Some of the insects
have tan bodies and some have green bodies. Over time, the habitat changes to
a grass-filled meadow. Use the ideas of natural selection to explain how and why
the insect population might change.
11. How does sexual reproduction affect a population’s genetic variation?
12. Identify two ways in which genes can be recombined during meiosis.
13. What is lateral gene transfer? How does it affect variation?
Single Gene and Polygenic Traits
14. Label the two graphs to show which represents a single-gene trait and which represents a
polygenic trait.
For Questions 15–19, write True if the statement is true. If the statement is false, change
the underlined word or words to make the statement true.
15. The number of phenotypes produced for a given trait depends on how
many genes control the trait.
16. Height in humans is an example of a single-gene trait.
270
17. Each gene of a polygenic trait often has two or more phenotypes.
18. A single polygenic trait often has many possible genotypes.
19. A symmetrical bell-shaped graph is typical of polygenic traits.
20. Use the Venn diagram to compare and contrast single-gene traits and polygenic traits.
Single-Gene Traits
Polygenic Traits
Both
Apply the Big idea
21. Why is genetic variation important to the process of evolution?
17.3 The Process of Speciation
Lesson Objectives
Identify the types of isolation that can lead to the formation of new species.
Describe the current hypothesis about Galápagos finch speciation.
Isolating Mechanisms
1. What is speciation?
2. What does it mean for two species to be reproductively isolated from each other?
3. What must happen in order for a new species to evolve?
4. List three ways that reproductive isolation occurs.
5. When does behavioral isolation occur?
6. When does geographic isolation occur?
7. What is an example of temporal isolation?
8. Suppose a seamount forms from an underwater volcano. Birds on the mainland colonize
the island. How might this lead to speciation?
Speciation in Darwin’s Finches
For Questions 9–13, complete each statement by writing the correct word or words.
9. Peter and Rosemary Grant spent years on the Galápagos Islands studying changes in
populations.
10. Many finch characteristics appear in bell-shaped distributions typical of
traits.
11. The ancestors of the Galápagos Island finches originally came from the continent of
.
12. The populations of finches on separate islands are
one another by large stretches of open water.
isolated from
13. Big-beaked finches that prefer to mate with other big-beaked finches are
isolated from small-beaked finches living on the same island.
14. Write a paragraph that summarizes how speciation likely occurred in the Galápagos
finches. Use the following terms in your response: geographic isolation, gene pools,
behavioral isolation, and competition.
Apply the Big idea
15. Explain why reproductive isolation must occur for separate populations of the same
species to evolve into different species.
17.4 Molecular Evolution
Lesson Objectives
Explain how molecular clocks are used.
Explain how new genes evolve.
Describe how Hox genes may be involved in evolutionary change
Timing Lineage Splits: Molecular Clocks
1. What is a molecular clock?
2. Why are only neutral mutations useful for molecular clocks?
3. Why are there many molecular clocks in a genome instead of just one?
Use the diagram of an ancestral species to
answer Questions 4–5. Each picture in the
diagram represents a gene. Each shaded
portion of a gene represents a mutation.
4. Which species is most closely related to
Species B? Explain your answer.
5. How can you tell that Species C is probably
not a descendant of the organism with Gene 2?
Gene Duplication
For Questions 6–7, write the letter of the correct answer on the line at the left.
6. Multiple copies of a duplicated gene can turn into a group of related genes called
A. globins.
B. duplicates.
C. a Hox gene.
D. a gene family.
7. A chromosome may get several copies of the same gene during the process of
A. crossing-over.
B. gene mutation.
C. gene expression.
D. artificial selection.
8. Complete the flowchart to show how a new gene can evolve from a duplicated gene.
Original gene
Exact copy of original gene
New gene evolves new
function.
Developmental Genes and Body Plans
9. What genetic factors might be responsible for a change in an organism’s body plan?
Apply the Big idea
10. How can Hox genes help reveal how evolution occurred?