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Unit 5 Study Guide
Chapters 22-25
Evolution
All questions within each section of the Unit Study Guide will be due on the day of the unit exam. Each
section should be clearly labeled by section number and number of question for complete points.
 5–1: Read 438—446
Natural Selection
 Pages 438 – 442 put Darwin’s ideas into historical context, no need to spend too much time on this
except: be able to state Lamarck’s idea of evolution.
 Taxonomy is the branch of biology dedicated to the naming and classification of all forms of life.
Carolus Linnaeus developed binomial nomenclature, a two-part naming system that includes the
organism’s genus and species.
 Jean-Baptiste de Lamarck developed an earl theory of evolution, which in part stated that
characteristics acquired during an organism’s lifetime could be passed on to the next generation.
Our modern understanding of genetics provides no evidence that this is possible.
 Darwin’s idea about how organisms evolve, natural selection, is highlighted in the yellow box on
page 444 and summarized later in the text. You must know this well!
 Darwin’s view of life as expressed in The Origin of Species (1859) contrasted sharply with
traditional beliefs of an Earth only a few thousand years old, populated by forms of life that has
been created at the beginning and remained unchanged ever since.
 The concept of natural selection states that a population can change over generation if individuals
with certain heritable traits produce more viable offspring than other individuals. The result of
natural selection is evolutionary adaptation, which is an accumulation of inherited characteristics
that enhance organisms’ ability to survive and reproduce in in specific environments.
 Natural Selection can work only on heritable traits, traits that are passed from organisms to their
offspring.
Questions:
1. Describe Lamarck’s view of evolution. How would you argue against it with your present knowledge
of genetics and molecular biology?
2. The word evolution was not used in Darwin’s publication; instead, he used “decent with
modification.” Explain what Darwin meant by this term.
3. Describe three inferences Darwin made from his observations that lead him to propose natural
selection as a mechanism for evolutionary change.
4. Thoroughly explain the concept of natural selection. Summarize with one sentence stressing the
most important idea in the theory of natural selection.
5. Explain why an individual organism cannot evolve.
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 5–2: Read 446—451
The Evidence
 As you read examples of natural selection, remember that it operates on chemical traits as well as
those more obviously visible.
 The section beginning with Homology. . . on page 448 describes what is sometimes referred to as “the
evidence for evolution by natural selection.” What is referred to as “molecular homology” is often
listed separately from the physical homology described in Fig 11.15. You should be able to define
these four categories of evidence, offer examples of each and state how it supports evolutionary
theory: Homologous structures, Vestigial organs, Molecular homology, Biogeography.
- Note: The fossil record is also considered to be evidence for evolution, as well, but in this
text it is mentioned separate and earlier in section 22.1.
 Darwin’s theory of evolution through natural selection explains the succession of forms in the fossil
record. Transitional fossils have been found that link ancient organisms to modern species, just as
Darwin’s theory predicts.
Questions:
1. Describe examples of natural selection.
2. List the four categories of, and explain, the evidence for evolution.
3. Do whales really need all those bones in their flippers? Explain.
4. In Fig 22.16, what conclusion can be reached about the relationship of humans to mice as
compared to that between humans and frogs?
5. How does a scientific theory differ from the general use of the term theory?
 5–3 Read 454—458
Hardy-Weinberg Equilibrium
 Be sure you understand the terms population, gene pool and, especially, allele frequency. Frequency is
usually expressed as a decimal quantity showing “parts out of one” (the total) but can also be
expressed as a percent (parts out of one hundred). Note that, in addition to allele frequencies, the
concept of frequency can also be applied to phenotypes and genotypes.
 You must know the Hardy-Weinberg theorem, the two equations describing it and how to do problems
involving allele frequencies.
 The Hardy-Weinberg theorem is used to describe a population that is NOT evolving. It states that
the frequencies of alleles and genes in a population’s gene pool will remain constant over the course of
generations unless they are acted upon by forces other than Mendelian segregation and the
recombination of alleles.
 Fig 23.5 is an example of how to apply the mathematics of Hardy-Weinberg. Notice that even though
the diagram looks like a Punnett square, it is referring to possible outcomes in an entire population
instead of possible offspring from a single pair of parents. The diagram should help you see how the
H-W math is used to calculate different frequencies. (At the top, we see the allele frequencies. At
the bottom, we see the frequency of the different genotypes.
 The yellow box, page 458, states the conditions for H-W equilibrium.
 Pedit states (old AP Bio teacher), “Every good biology student knows these [H-W conditions] or dies
slowly on tests, flounders in misunderstanding and gives birth to half-baked children whose only
dream is to join the circus.” (hahaha, I saw this on one of Mr. Pedit’s old worksheets and thought it
was hilarious!)
 HARDY-WEINBERGY WILL BE ON YOUR AP EXAM!!! KNOW THE MECHANISMS AND
MATHEMATICAL APPLICATIONS!!!!!!!
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Questions 5-3:
1. Describe the Hardy–Weinberg equilibrium in words and with mathematics.
2. State the conditions are necessary for the Hardy–Weinberg equilibrium to hold true.
3. Use the H-W equation to calculate allele frequencies when the frequency of homozygous recessive
individuals in a population is 25%
4. Explain why meiosis and random fertilization alone will not alter the frequency of alleles or
genotypes in a population.
 5–4: Read 459—470
Microevolution
 Today we define evolutionary change on it smallest scale as microevolution. Microevolution is change
in the genetic makeup of a population from generation to generation. It refers to adaptations that
are confined to a single gene pool.
 New genes and new alleles originate only by mutations, which are changes in the nucleotide sequence
of DNA. Because mutations in somatic cells disappear when the individual dies, only mutations in
somatic cells disappear when the individual dies, only mutations in cell lines that produce gametes can
be passed to offspring.
 Mutation has two roles. It is a H-W factor and can contribute to changes in gene frequencies. But it
also has the all-important role of adding new alleles and genes to populations. Recombination is also
important in bringing new combinations of existing alleles together for yet more variation for natural
selection to act upon.
 Natural selection is, by far, the most important H-W factor. Why?
 Genetic drift is also quite important, especially when considering how a new population might get
established. Genetic drift is the unpredictable fluctuation in allelic frequencies from one generation
to the next. The smaller the population, the greater the chance is for genetic drift.
 Examples of genetic drift:
- Bottleneck effect = sudden change in environment (ex. earthquake, flood, fire) drastically reduces
the size of a population. The few survivors that pass through the restrictive bottleneck may have
a gene pool that no longer reflects the original population’s gene pool.
- Founder effect = occurs when a few individuals become isolated from a larger population and
establish a new population whose gene pool is not reflective of the source population.
 Section 23.4 makes an important point but is a bit long winded. Read lightly to get the idea; focus on:
- Figures 23.11 and 23.12
- “Heterozygous Advantage”, page 466
- Page 469, “Why Natural Selection. . .”. Notice the role of genetic drift.
Questions:
1. List and explain the five factors that can shift the Hardy–Weinberg equilibrium (= causes of
microevolution).
2. Which factor do you think is most important? Why?
3. Genetic variation: what is it, what are the sources, how is it maintained?
4. Explain how, and upon what, natural selection acts and with what results.
5. Explain how diploidy can protect a rare recessive allele from elimination by natural selection.
6. Explain what is meant by heterozygote advantage and give an example. How does this affect allele
frequencies?
7. Is all selection done by environmental factors? Explain.
8. Explain how female preferences for showy male traits may benefit the female.
9. Explain how the genetic variation promoted by sex may be advantageous to individual on a
generational time scale.
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 5–5: Read 472—480 [up to “Adaptive Radiation”]
Speciation
 Speciation is the process by which new species arise.
 Fig 24.2: don’t sweat the terms. The difference is the left side shows the formation of a new species
over time. The right show how one species can eventually produce two separate species.
 This chapter is about how enough changes (or even the right single change) can result in speciation. To
understand this, you need to know what is meant by species.
 Since species are different due to different alleles (and entire genes if more distantly related), then
something has to prevent the alleles from mixing (“gene flow”) if two species are to develop from one.
The populations, or sub=populations, that are to go on to become different species must be
reproductively isolated. This is the key. Different types of reproductive barriers are shown in Fig.
24.4: Focus on the “prezygotic barriers”, have a passing knowledge of the postzygotic barriers.
 Skim the sections on Polyploidy and Habitat Differentiation.
 But, do be able to distinguish between, and give examples of, allopatric and sympatric speciation.
Questions:
1. Define species in the biological sense. What problems exist with this definition?
2. List and explain five mechanisms that can isolate populations. (You can consider the postzygotic
barriers together.)
3. Describe the process through which allopatric speciation and sympatric speciation may occur.
4. Give an overview as to the necessary conditions for speciation to occur.
 5–6: Read 480—488
Macroevolution
 Adaptive radiation is what started it all (i.e., Darwin’s finches).
 Adaptive radiation occurs when many new species arise from a single common ancestor. It typically
occurs when a few organisms make their way to new, distant areas or when environmental changes
cause numerous extinctions, opening up ecological niches for the survivors.
 Section 24.3 adds nothing new as far as basic concepts. Macroevolution simply refers to the same
evolutionary principles acting over very long periods of time to produce large changes. The main
addition might be this: although recombination might be enough to produce speciation, the great
diversity of life seen today also requires mutations and chromosomal rearrangements.
 Early arguments against evolutionary theory centered around: How could something as complicated as
the eye, obviously requiring many genes, “evolve” when many different evolutionary events are
required and unlikely to have all occurred together. Fig 24.14 shows that it doesn’t take a complete
modern eye to offer some adaptive function. Can you think of how just the “patch of pigmented cells”
shown in (a) might be advantageous?
 Pay special attention to Evolution is Not Goal Oriented (using Fig 24.20 as an example). How does this
apply to the eye in Fig 24.14?
 Punctuated equilibrium is a term used to describe periods of apparent stasis punctuated by sudden
change observed in the fossil record.
 Homeotic genes determine the location of and organization of body parts. Hox genes are one class of
homeotic genes. Changes in Hox genes and in the genes that regulate them can have a profound
effect on morphology, thus contributing to the potential for evolutionary change.
Questions:
1. What is meant by punctuated equilibrium? What might this have to do with so called “gaps” in the
fossil record?
2. Describe how each step in the evolution of the complex eye might bestow an evolutionary
advantage to its owner.
3. How do the roles of natural selection and genetic drift figure into the discussion of evolution not
being goal oriented?
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 5–7: Read 491—508
Classification and Phylogeny
 Fig 25.2: whoa! By now you should be able to read the thick green lines as saying: humans share a more
recent common ancestor with fungi than they do with plants. Must be due to something more
fundamental that outward appearance.
 You should be able to distinguish analogous structures from homologous structures and offer
examples of each. Understand why each arises.
 Convergent evolution has taken place when two organisms developed similarities as they adapted to
similar environmental challenges – not because they evolved from a common ancestor. The likenesses
that result from convergent evolution are considered analogous rather than homologous. For example,
the four-chambered heart of birds and mammals is analogous. The most recent common ancestor of
birds and mammals had a three-chambered heart.
 The comparison of different genes and proteins (molecular systematics) of organisms allows us to
determine evolutionary relationships on a molecular level. The more alike the DNA sequences of two
organisms are, the more closely related they are evolutionarily.
 Fig 25.8 outlines the system of classifying organisms into broader, more inclusive groups (going down
the chart). But Fig 25.9 puts some meaning on the usefulness of classifying in this way. Be sure you
understand this and the two related diagrams in the text.
 The hierarchical classification of organisms consists of the following levels (in order of decreasing
broadness): domain, kingdom, phylum, class, order, family, genus, species
 Focus on the section on Cladistics including Fig’s 25.10 and 25.11(b).
 Skim 499 – 507 [The Universal. . .] except for these points:
- In fig 25.13, note how times since the common ancestor can be found from the fossil record and
using “molecular clocks”
- Fig 25.17 serves as a reminder of how new genes can develop fueling evolution.
- Briefly know what a molecular clock is.
 Fig 25.18 is even more shocking than Fig 25.2. Read this sub-section in detail
 Molecular clocks are methods used to measure the absolute time of evolutionary change based on the
observation that some genes and other regions of the genome appear to evolve at constant rates.
Questions:
1. List the levels of classification. Which are used to name organisms?
2. Compare and contrast homology and analogy. Explain why it is crucial to distinguish between
homology and analogy before selecting characters to use in the reconstruction of phylogeny.
3. How can proteins and DNA be used to compare species?
4. Does the apparent discontinuity of the fossil record (e.g.: horses) bother biologists? Explain.
5. What is the defining characteristic of a cladogram? What advantage does cladistics offer over
earlier methods of classifying critters?
6. Describe the evidence that suggests there is a universal tree of life.
7. Explain how molecular clocks are used to determine the approximate time of key evolutionary
events. Explain how molecular clocks are calibrated in actual time.
8. Describe some limitations of molecular clocks.
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