Download 15 evolution on a small scale

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15
EVOLUTION
ON A
SMALL SCALE
CHAPTER REVIEW
Darwin had no knowledge of genetics and all his work pertained to phenotypic changes rather than genotypic
changes. Later, investigators saw how it was possible to
tell genetically that evolution had occurred. First, we
must consider the gene pool of a population—after all,
populations evolve and not individuals. When allele gene
pool frequencies change, evolution has occurred.
This chapter also studies natural selection with regard to both genotypic and phenotypic changes within a
population. The phenotypes follow a bell-shaped curve
because most traits of evolutionary significance are polygenic. Even after natural selection has occurred, the phenotypes within a population still vary along a continuum.
CHAPTER KEY TERMS
After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms.
assortative mating
microevolution
bottleneck effect
mutation
directional selection
natural selection
disruptive selection
nonrandom mating
founder effect
polymorphism
gene flow
population
gene pool
sexual selection
genetic drift
stabilizing selection
industrial melanism
a. type of genetic drift when only a few people of an original population begin a new population
_______________________
b. total of all genes of all the individuals in a population _______________________
c. adaptation caused by environmental selection of fittest _______________________
d. several distinct phenotypes in a population _______________________
e. tendency to mate with those that have the same phenotype _______________________
f. change in gene pool frequencies within a population over time _______________________
g. type of genetic drift when the majority are prevented from reproducing, usually by a catastrophe
_______________________
h. increased frequency of darkly pigmented forms due to pollution _______________________
i. outcome of natural selection when the intermediate phenotype increases _______________________
j. the raw material for evolutionary change _______________________
k. natural selection in two extreme phenotypes exist because the average phenotype is not favored
_______________________
l. changes in gene pool frequencies of a population due to chance events _______________________
m. group of organisms of the same species occupying a certain area; share a common gene pool _______________________
n. natural selection in which a single extreme phenotype is favored _______________________
o. changes in male and female behavior and anatomy leading to increased fitness _______________________
p. mating among individuals, not by chance, but on the basis of their phenotype _______________________
q. sharing of genes between two populations _______________________
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S T U DY E X E R C I S E S
Study the text section by section as you answer the following questions.
15.1 MICROEVOLUTION (PP. 232–238)
•
•
•
•
Microevolution occurs when allele frequencies change from one generation to the next.
The Hardy-Weinberg principle describes a nonevolving population in terms of allele frequencies.
The raw material for microevolutionary change is mutations.
Mutations, gene flow, nonrandom mating, genetic drift, and natural selection can cause allele frequency
changes in a population.
1. What are the different gene pool frequencies of a population? The percent of the population that is
a. __________________, b. __________________, or c. __________________ and the percent of d. ______________
alleles and e. ______________ alleles.
2. Imagine a population of fruit flies that are reproducing sexually but with no mutations, no gene flow, no
genetic drift; no selection occurs and mating is random. Will evolution, defined as a change in gene pool
frequencies, occur? Explain. ________________________________________________________________________
3. Considering the equation p 2 + 2 pq + q 2 , match each of the following with either aa, a, A, AA, or Aa.
a. p 2 = ______________.
b. p = ______________.
c. 2pq = ______________.
d. q 2 = ______________.
e. q = ______________.
In questions 4–6, give your answers in decimals:
4. An investigator determines, by inspection, that 4% of a population is albino. Answer the following questions
about this population:
a. q 2 = ______________.
b. This represents the percentage of the population that is ______________.
c. What is the frequency of the recessive allele in this population? q = ______________
d. Considering the frequency of the recessive allele, what is the frequency of the dominant allele?
p = ______________
e. If p = this value, then p 2 = ______________.
f. This is the frequency of the population that is ______________.
g. The value of 2pq = ______________.
h. This represents the frequency of the population that is ______________.
i. What percentage of the population has normal pigmentation? ______________
5. 49% of a population cannot taste a chemical called PTC. Presence of a dominant allele is necessary to taste
this substance. Complete the following information about the gene pool of the population:
a. q 2 = ______________
b. q = ______________
c. p = ______________
d. p 2 = ______________
e. 2pq = ______________
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6. a. Using this Punnett square, show that the next generation of the population in question 5 will have exactly
the same composition, assuming a Hardy-Weinberg equilibrium if T is the dominant allele and t is the
recessive allele.
(
)T
(
)t
(
)T
(
)TT
(
)Tt
(
)t
(
)Tt
(
)tt
b. Describe the gene pool of the next generation. ______________________________________________________
c. The frequency of T = ______________.
d. The frequency of t = ______________.
e. How would we know when evolution occurs? ______________________________________________________
7. Label the statements with the correct agents of evolutionary change:
gene flow
genetic drift
mutations
natural selection
nonrandom mating
a.
Investigators have discovered that multiple alleles are common in a population.
b.
Populations are subject to new alleles entering by the migration of organisms
between populations.
c.
Female birds of paradise choose mates with the most splendid feathers.
d.
Investigators discovered that if they randomly picked out a few flies from each
generation to start the next generation, gene pool frequency changes appeared.
e.
Giraffes with longer necks get a larger share of resources and tend to have more
offspring.
8. Match these descriptions to one of the agents of evolutionary change listed in question 7. Some agents are
used more than once:
a.
Dwarfism is common among the Amish of Lancaster County, Pennsylvania.
b.
Cheetahs are homozygous for a larger proportion of their genes.
c.
This agent of change tends to make the members of a population dissimilar to one
another.
d.
This agent of change tends to make the members of a population similar to one
another.
e.
Certain members of a population are more fit than other members.
f.
Bacteria and insects become resistant to agents that formerly killed them.
9. Indicate whether these statements, related to sources of variation among diploid members in a population, are
true (T) or false (F).
a.
Genetic mutations occur at random.
b.
The only mutations that occur are those that make organisms more fit (able to produce more
offspring than other members of the population).
c.
Some chromosomal mutations are simply a change in chromosomal number.
d.
An offspring receives recombined genes because of the events of gametogenesis and fertilization.
e.
Recombination is a significant source of variation because many traits are polygenic.
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15.2 NATURAL SELECTION (PP. 238–242)
• Natural selection causes changes in allele frequencies in a population due to the fitness of certain phenotypes
to reproduce.
• Natural selection results in adaptation to the environment. The three types of natural selection are directional
selection, stabilizing selection, and disruptive selection.
10. Natural selection can now be understood in terms of genetics. Many of the variations (phenotypes) that exist
between members of a population are due to differences in a. ______________. Some of these genotypes result
in b. ______________ to the environment. Individuals better adapted to the environment reproduce to a(n)
c. ______________
extent, and therefore, these genotypes and phenotypes become more prevalent in
the population.
11 . Match the observations to the correct type of natural selection at work:
directional
disruptive
stabilizing
a.
Trees in a windy area tend to remain the same size each year.
b.
The brain size of hominids steadily increases.
c.
The same species of moths tends to have blue stripes in open areas and orange
stripes in forested areas.
12. Match the types of natural selection listed in question 11 with the following diagrams:
a.
b.
c.
13. Variation is maintained in a population despite directional and stabilizing selection when members have
a. ______________
alleles for every trait. That’s because the b. ______________ allele is hidden by the
c. ______________
allele. In instances such as sickle cell disease, in which the d. ______________ genotype is
more fit, the two e. ______________ genotypes are maintained.
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K E Y WO R D C RO S S WO R D
Review key terms by completing this crossword puzzle, using the following alphabetized list of terms:
1
2
3
4
5
6
7
assortative
founder effect
gene flow
gene pool
genetic drift
microevolution
mutation
natural selection
nonrandom
population
8
9
Across
1 environmental selection of most fit organisms to
reproduce
4 tendency for a new, small population to have a different gene pool from the original, larger population (two words)
7 alternation in a gene due to a change in DNA composition
8 change in gene frequencies within a population over
time
9 total of all the genes of all the individuals in a population (two words)
128
Down
1 mating among individuals on the basis of their phenotypic similarities or differences
2 type of mating; those with the same phenotype tend
to mate
3 sharing of genes between two populations due to migration (two words)
5 change in the genetic makeup of a population due
to chance (random) events; important in small populations (two words)
6 group of organisms of the same species occupying
a certain area and sharing a common gene pool
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CHAPTER TEST
OBJECTIVE QUESTIONS
Do not refer to the text when taking this test.
In questions 1–5, assume that 16% of the organisms in a
population are homozygous recessive. Describe the current gene pool.
1. frequency of aa
2. frequency of a
3. frequency of A
4. frequency of AA
5. frequency of Aa
6. Each is a condition of the Hardy-Weinberg principle EXCEPT
a. gene flow is absent.
b. genetic drift does not occur.
c. mutations are lacking.
d. random mating does not occur.
7. Establishment of polydactylism among the Amish
is an example of
a. artificial selection.
b. natural selection.
c. the bottleneck effect.
d. the founder effect.
8. Industrial melanism is an example of selection
that is
a. directional.
b. disruptive.
c. sexual.
d. stabilizing.
9. In a population of mature trees, disruptive selection
a. always favors the shortest trees only.
b. always favors the tallest trees only.
c. occurs if the environment is diverse.
d. will occur in an uniform environment.
10. Each factor contributes to the maintenance of
variation due to a recessive allele EXCEPT
a. diploidy.
b. heterozygosity.
c. homozygosity.
d. sexual reproduction.
11. The frequency of the dark form of the peppered
moth increased in industrial areas of England
during the nineteenth century. This is because
a. predatory birds changed their preference from
the light to the dark form.
b. the light form was more sensitive to deteriorating environmental conditions.
c. dark-colored moths had a better survival rate
as the Industrial Revolution progressed.
d. environmental pollutants became responsible
for increased mutation rates.
e. the allele for dark color is dominant to that
for light color.
12. Evolution by natural selection requires
a. variation.
b. heritable genetic differences.
c. differential adaptedness.
d. differential reproduction.
e. All of these are correct.
13. Which of these is consistent with the HardyWeinberg principle?
a. Sexual reproduction does not cause evolution.
b. Nonrandom mating can cause microevolution.
c. Genetic changes over time can cause evolution.
d. Recessive alleles do not tend to disappear over
time.
e. All of these are correct.
14. Changes in allele frequencies that lead to adaptation to a particular environment are due to
a. selective selection.
b. natural selection.
c. genetic drift.
d. gene flow.
15. Mutations
a. are the raw material for evolution.
b. are the cause of variations between members
of a population.
c. occur because of natural selection.
d. are always beneficial.
e. Both a and b are correct.
16. Individuals with a phenotype near the mean are
favored in this type of natural selection.
a. disruptive selection
b. sexual selection
c. stabilizing selection
d. directional selection
17. The survival of a human with the genotype
Hb A Hb S demonstrates
a. natural selection does not work.
b. common descent does occur.
c. heterozygote superiority.
d. mutations are favorable.
18. Which of the following statements is NOT true
of natural selection?
a. Natural selection directs the course of evolution by bringing about certain mutations.
b. The offspring of individuals that are better
adapted usually have more offspring.
c. Natural selection depends on genetic variability and, therefore, on mutations.
d. Natural selection usually preserves characteristics suitable to a particular environment.
e. Both a and d are not true.
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CRITICAL THINKING QUESTIONS
The introduction to this chapter is about sexual selection.
19. Sexual selection is a form of nonrandom mating. Why? ______________________________________________________
20. Why does nonrandom mating contribute to evolution? _______________________________________________________
21. Male competition wouldn’t survive unless it resulted in what? _______________________________________________
22. Let’s assume that male peacocks became increasingly showy due to female choice. Is this a form of natural
selection or artificial selection? Why? ______________________________________________________________________
Test Results: ______ number correct ÷ 22 = ______ × 100 = ______ %
EXPLORING
THE
INTERNET
ARIS, the Essentials of Biology website: http://www.mhhe.com/maderessentials
ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological
concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter.
There is even an online tutorial service!
ANSWER KEY
CHAPTER KEY TERMS
a. founder effect b. gene pool c. natural selection
d. polymorphism e. assortative mating f. microevolution
g. bottleneck effect h. industrial melanism i. stabilizing
selection j. mutation k. disruptive selection l. genetic
drift m. population n. directional selection o. sexual selection p. nonrandom mating q. gene flow
fect) c. mutations d. natural selection e. mutations
f. natural selection 9. a. T b. F c. T d. T e. T
10. a. genotypes b. adaptations c. greater 11. a. stabilizing b. directional c. disruptive 12. a. directional
b. stabilizing c. disruptive 13. a. two b. recessive
c. dominant d. heterozygous e. homozygous
KEYWORD CROSSWORD
1
N
STUDY EXERCISES
A
T
U
R
N
1. a. homozygous dominant b. heterozygous c. homozygous recessive d. dominant e. recessive 2. No,
because sexual reproduction in and of itself does not
bring about gene pool frequencies. 3. a. AA b. A
c. Aa d. aa e. a 4. a. 0.04 b. homozygous recessive
c. 0.2 d. 0.8 e. 0.64 f. homozygous dominant g. 0.32
h. heterozygous i. 0.96 5. a. 0.49 b. 0.7 c. 0.3
d. 0.09 e. 0.42
6. a.
(0.3)T
(0.7)t
(0.3)T
(0.09)TT
(0.21)Tt
(0.7)t
(0.21)Tt
(0.49)tt
2
A
F
5
O
N
E
T
D
N
A
O
E
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T
M
L
E
C
T
I
O
N
3
I
C
G
U
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D
E
R
E
F
F
T
I
O
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C
T
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6
F
P
O
N
V
R
E
N
T
A
I
8
E
R
G
A
M
S
S
4
R
7
L
S
O
V
O
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O
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P
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I
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P
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A
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CHAPTER TEST
b. In the next generation, p 2 = 0.09, 2pq = 0.42, q 2 = 0.49;
this is exactly the same as the parental generation in question 5. c. 0.3 d. 0.7 e. when gene pool frequencies
change 7. a. mutations b. gene flow c. nonrandom
mating d. genetic drift e. natural selection 8. a. genetic drift (founder effect) b. genetic drift (bottleneck ef-
130
1. 0.16 = 16% 2. 0.4 3. 0.6 4. 0.36 = 36% 5. 0.48
= 48% 6. d 7. d 8. a 9. c 10. c 11. c
12. e 13. e 14. b 15. e 16. c 17. c 18. a
19. Because of male competition and female choice, some
males don’t mate or they mate infrequently. 20. Allele
frequencies will change in the next generation. 21. increases fitness 22. artificial selection, with females
being the selecting agent