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Chapter 22: Descent with Modification
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Chapter 22: Descent with Modification: A Darwinian View of Life
As you study this chapter, read several paragraphs at a time to catch the flow of ideas and understand the
reasoning that is being described. In some places, the text describes a narrative or story of events that led
to Darwin’s theory of evolution. Therefore, first read the narrative to absorb the big picture and then
return to answer the few questions that accompany this material.
Overview
1. Define evolution broadly and then give a narrower definition, as discussed in the overview.
Concept 22.1 The Darwinian revolution challenged the traditional view of a young Earth inhabited
by unchanging species
2. Jean-Baptiste de Lamarck proposed a mechanism for how life changes over time. Explain the two
principles of his mechanism.
use and disuse
inheritance of acquired characteristics
3. Although Lamarck’s mechanism of evolution does not explain the changes in species over time,
his thinking has been influential. What is considered to be the great importance of his ideas?
Concept 22.2 Descent with modification by natural selection explains the adaptations of organisms
and the unity and diversity of life
4. Charles Darwin proposed that the mechanism of evolution is natural selection and that it
explains how adaptations arise. What are adaptations? Give two examples of adaptations.
Chapter 22: Descent with Modification
5. Explain the process of natural selection by summarizing Darwin’s observations that drive changes in
species over time:
Observation
1. Variations in traits exist.
Explanation
2. These variations (traits) are heritable.
3. Species overproduce.
4. There is competition for resources;
not all offspring survive.
6.
From these four observations, which two inferences did Darwin make?
7.
It is important to remember that differences in heritable traits can lead to differential
reproductive success. This means that the individuals who have the necessary traits to promote
survival in the current environment will leave the most offspring. What can this differential
reproductive success lead to over time?
8.
To demonstrate your understanding of this section, complete the following sentences:
do not evolve.
evolve.
Now, take out your highlighter and mark the information in the box above. Hold these ideas firmly in
your brain! Finally, if you are ever asked to explain Darwin’s theory of evolution by natural selection
(a common AP essay question), do not pull out the phrase “survival of the fittest.” Instead, cite the
points made in question 5 and explain the inferences that are drawn from them.
Concept 22.3 Evolution is supported by an overwhelming amount of scientific evidence
9. How does the fossil record give evidence for evolution?
Chapter 24: The Origin of Species
10. What is meant by each of the following terms? Give an example of each.
Term
Homologous structures
Definition
Example
Vestigial structures
Analogous structures
11. How do homologous structures give evidence for evolution?
12. What is summarized in an evolutionary tree?
13. Figure 22.17 shows an evolutionary tree. What is indicated by each branch point or “node”?
Mark each branch point.
14. What is indicated by the hatch marks? ________________________________________________
15. Use the tree below to answer this
question: Are crocodiles more closely related
to lizards or to birds? Explain your response.
16. On the evolutionary tree, label the
vertical lines to the right, and annotate the
key feature that marks each group.
17.
Organisms that are only distantly related can resemble each other. Explain convergent
evolution, and describe how analogous structures can arise.
18.
Convergent evolution might be summarized like this: Similar problem, similar solution. Can
you give two examples of convergent evolution?
Chapter 24: The Origin of Species
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Chapter 23: The Evolution of Populations
This chapter begins with the idea that we focused on as we closed the last chapter: Individuals do not
evolve! Populations evolve. The Overview looks at the work of Peter and Rosemary Grant with
Galápagos finches to illustrate this point, and the rest of the chapter examines the change in
populations over time. As in the last chapter, first read each concept to get the big picture and then go
back to work on the details presented by our questions. Don’t lose sight of the conceptual
understanding by getting lost in the details!
Overview
1.
What is microevolution?
2.
What are the three main mechanisms that can cause changes in allele frequency?
3.
Which is the only mechanism that is adaptive, or improves the match between organisms and
their environment?
Concept 23.1 Mutation and sexual reproduction produce the genetic variation that makes evolution
possible
4.
What is the ultimate source of new alleles?
5.
Mutations are any change in the nucleotide sequence of an organism’s DNA. These
mutations provide the raw material from which new traits may arise and be selected. What occurs
in a point mutation?
6.
What is translocation? How could it be beneficial?
7.
Much of the genetic variation that makes evolution possible comes through sexual
reproduction. What are the three mechanisms by which sexual reproduction shuffles existing
alleles?
Chapter 24: The Origin of Species
Concept 23.2 The Hardy-Weinberg equation can be used to test whether a population is evolving
8.
What is a population?
9.
What is a gene pool?
10.
The greater the number of fixed alleles, the lower the species’ diversity. What does it mean to
say that an allele is fixed?
11.
The Hardy-Weinberg principle is used to describe a population that is not evolving.
What does this principle state?
12.
If the frequency of alleles in a population remains constant, the population is at HardyWeinberg equilibrium. There are five conditions for Hardy-Weinberg equilibrium. It is very
important for you to know these conditions, so enter them neatly into the box below.
CONDITIONS FOR HARDY-WEINBERG EQUILIBRIUM
1.
2.
3.
4.
5.
It is not very likely that all five of these conditions will occur, is it? Allelic frequencies change.
Populations evolve. This data can be tested by applying the Hardy Weinberg equation.
We will do this together in class, but start to get comfortable with the equation and it’s variables now!
Equation for Hardy-Weinberg Equilibrium
p2 + 2pq + q2 = 1
Where p2 is equal to the frequency of the homozygous dominant in the population, 2pq is equal to
the frequency of all the heterozygotes in the population, and q2 is equal to the frequency of the
homozygous recessive in the population.
Chapter 24: The Origin of Species
Concept 23.3 Natural selection, genetic drift, and gene flow can alter allele frequencies in a
population
First, let’s try to summarize the big idea from this section. Scan through the entire concept to
pull out this information. Three major factors alter allelic frequency and bring about
evolutionary change. List each factor, and give an explanation.
13.
Factor
Explanation
14.
Which of the factors above results in a random, non-adaptive change in allelic frequencies?
15.
Which of the factors above tends to reduce the genetic differences between populations and
make populations more similar?
16.
Of the three factors you listed above, only one results in individuals that are better suited to
their environment. Which is it? _________________________________________
17 .
Explain what happens in each of these examples of genetic drift:
founder effect 
bottleneck effect 
Concept 23.4 Natural selection is the only mechanism that consistently causes adaptive evolution
18.
In evolutionary terms, fitness refers only to the ability to leave offspring and contribute to the
gene pool of the next generation. It may have nothing to do with being big, or strong, or
aggressive. Define relative fitness.
19.
What is the relative fitness of a sterile mule?
Chapter 24: The Origin of Species
20.
Figure 23.13 is important because it helps explain the three modes of selection. Label each type of
selection, and fill in the chart to explain what is occurring.
Type of Selection How It Works
Stabilizing
Directional
Disruptive
21. Discuss what is meant by heterozygote advantage, and use sickle-cell anemia as an example.
22. Finally, give four reasons why natural selection cannot produce perfect organisms.
Chapter 24: The Origin of Species
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Chapter 24: The Origin of Species
Overview
1.
Define speciation.
2.
Distinguish between microevolution and macroevolution.
Concept 24.1 The biological species concept emphasizes reproductive isolation
3.
Use the biological species concept to define species.
4.
What is required for the formation of new species?
5.
What are hybrids?
6.
Explain the two types of barriers that maintain reproductive isolation.
7.
The following charts summarize the various ways that reproductive isolation is maintained.
Explain and give an example of each type of isolating mechanism.
Prezygotic Reproductive
Barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Explanation
Example
Chapter 24: The Origin of Species
Postzygotic
Reproductive Barriers
Explanation
Example
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
8.
The concept of reproductive isolation is essential for an understanding of speciation, so we are
going to have you look at it again. Refer to Figure 24.3, and label the sketch below. Name each type
of isolating mechanism.
Concept 24.2 Speciation can take place with or without geographic separation
9. Gene flow can be interrupted in two main ways. Explain and give an example of each by labeling and
annotating this figure, which shows allopatric or sympatric speciation.
fish
Chapter 24: The Origin of Species
10. Sympatric speciation occurs in populations that live in the same geographic area. How is this
possible?
11. Your response to question 12 should have listed polyploidy, habitat differentiation, and
sexual selection. Explain what happens in sexual selection, and how this process can drive
sympatric speciation.
Concept 24.4 Speciation can occur rapidly or slowly, and it can result from changes in few or many
genes
12.
Stephen Jay Gould and Niles Eldredge coined the term punctuated equilibria. What is meant by
a punctuated pattern?
13.
This figure shows 2 different views of speciation. Label this figure, and explain how each of
the pictures explains speciation.
Chapter 25: The History of Life on Earth
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Chapter 25: The History of Life on Earth
Overview
1.
In the last chapter, you were asked about macroevolution. To begin this chapter, give some
examples of macroevolution. Include at least one novel example not in your text.
Concept 25.1 Conditions on early Earth made the origin of life possible
2.
How old is the planet?
How old is the earliest evidence of life on Earth?
3.
The current theory of the origin of life suggests a sequence of four main stages. Summarize them
here.
1.
2.
3.
4.
4.
In your chart above, the first stage is the synthesis of organic molecules. Consider the early
planet, probably thick with water vapor and stinky with methane, ammonia, and hydrogen
sulfide. What gas was missing from this early mix? _________________________
5.
A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing
environment. What did they suggest was the source of energy for the early organic synthesis?
Chapter 25: The History of Life on Earth
Haldane hypothesis with this apparatus. (It is shown in Chapter 4, Figure 4.2, so you have seen it
before.) Explain the elements of this experiment, using arrows to indicate what occurs in various
parts of the apparatus.
7.
What was collected in the sample for chemical analysis? What was concluded from the results of
this experiment?
8.
What did Thomas Cech propose was the first genetic material, DNA or RNA?
9.
What are ribozymes?
10.
Explain the evidence for an early “RNA world.”
Concept 25.3 Key events in life’s history include the origins of single-celled and multicelled
organisms and the colonization of land
13.
What was the earliest form of life on the planet? How long ago did this life-form first occur?
14.
What unique ability was originated with cyanobacteria? How did this alter life on Earth and
lead to a wave of mass extinctions?
15. The first eukaryotes did not appear until approximately 2.1 billion years ago. What is the name of
the theory that explains the evolution of eukaryotes? ____________________________