Download Chapter 27: Evolutionary Genetics

Chapter 27: Evolutionary Genetics
Student Learning Objectives
Upon completion of this chapter you should be able to:
1. Understand what the term species means to biology.
2. Recognize the various patterns of speciation and the factors that contribute to each.
3. Understand the concept of phylogenetic trees, and the basic principles of their
formation.
4. Analyze phylogenetic trees.
5. Know the principles of the neutral theory of evolution.
6. Understand the concept of the molecular clock.
7. Recognize the key role that certain proteins have played in promoting the
morphological changes that occur during evolution.
27.1 Origin of Species
Overview
The final chapter of the text examines the phenotypic changes that occur during evolution
and their underlying genetic causes. The first section focuses on the general features of evolution
as it occurs in natural populations over time. It begins with a discussion of the most commonly
used characteristics to distinguish species. These include morphological traits (Figure 27.1),
ability to interbreed (Table 27.1), molecular features, ecological factors, and evolutionary
relationships. The section then turns to speciation – the process by which new species are formed
via evolution. It may occur by anagenesis, when one species evolves into a new one, or more
commonly by cladogenesis, in which a species diverges into two or more different species (Refer
to Figure 27.2). The section ends with a discussion of the three forms of cladogenesis: allopatric,
parapatric, and sympatric speciation.
Outline of Key Terms
Speciation
Anagenesis
Cladogenesis
Allopatric speciation
Founder effect
Parapatric speciation
Hybrid zones
Sympatric speciation
Biological evolution
Macroevolution
Microevolution
Molecular evolution
Species
Subspecies
Ecotypes
Species concepts
Biological species concept
Reproductive isolation
Prezygotic mechanisms
Postzygotic mechanisms
Evolutionary lineage concept
General lineage concept
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Focal Points
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

Concepts of species (pages 681-684)
Types of reproductive isolation (Table 27.1)
Comparison between anagenesis and cladogenesis (Figure 27.2)
Allopatric, parapatric, and sympatric speciation (Table 27.2)
Comparison of crosses between three species with different ploidy levels (Figure 27.4)
Exercises and Problems
For questions 1 to 6, choose the term that best describes the statement.
_____ 1. Each species is a population of an independently evolving lineage.
_____ 2. Examples include habitat isolation and mechanical isolation.
_____ 3. Examples include hybrid inviability and hybrid sterility.
_____ 4. A single species is transformed into another species over time.
_____ 5. A group of individuals who have the potential to interbreed and produce viable,
fertile offspring.
_____ 6. The division of an original species into two or more separate species.
a.
b.
c.
d.
e.
f.
biological species concept
prezygotic isolating mechanisms
cladogenesis
general lineage concept
postzygotic isolating mechanisms
anagenesis
For questions 7 to 12, choose the pattern of divergent evolution that is best described by the
statement.
a. parapatric speciation
b. sympatric speciation
c. allopatric speciation
_____ 7.
May occur as a result of founder effect.
_____ 8.
Occurs as a result of partial separation of two species.
_____ 9.
Polyploidy in plants is an example.
_____ 10. Occurs with two species that occupy the same habitat or range.
_____ 11. Occurs as a result of geographic separation.
_____ 12. Hybrid zones are a characteristic of this model.
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27.2 Phylogenetic Trees
Overview
Phylogeny refers to the sequence of events involved in the evolutionary development of a
species or group of species. A phylogenetic tree is basically a diagram that describes a phylogeny
(Figure 26.6). This section examines the construction and analysis of phylogenetic trees. The text
focuses on cladistics (pages 739-741), which compares traits (or characters), that are either shared
or not shared by different species. The text also describes how the validity of possible trees can be
evaluated by the principle of parsimony, maximum likelihood, and Bayesian methods. The
discussion then moves to how phylogenetic trees have helped refine our understanding of
evolutionary relationships between organisms. For example, analysis of 16S and 18S rRNA
sequences by Carl Woese in 1977, enabled him to discover a new domain of life called Archaea
(Figure 26.9). Moreover, recent molecular genetic data have shed new light on the classification
of species (Figure 26.10). Finally, the section addresses the role of horizontal gene transfer in the
evolution of life (Figure 26.11).
Outline of Key Terms
Bacteria
Archaea
Eukarya
Supergroups
Vertical evolution
Horizontal gene transfer
Phylogeny
Systematists
Phylogenetic tree
Monophyletic group
Clade
Homology
Homologous genes
Cladistic approach
Cladogram
Ancestral (primitive) characters
Shared derived characters
Synapomorphy
Ingroup
Outgroup
Principle of parsimony
Maximum likelihood
Bayesian methods
Focal Points




How to read a phylogenetic tree (Figure 27.5)
Cladistics (pages 689-690) and phenetics (pages 690-692)
A modern cladogram for eukaryotes (Figure 27.9)
A revised view regarding the evolution of life (Figure 27.10)
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Exercises and Problems
Complete the following sentences with the most appropriate word or phrase.
1. A monophyletic group, also known as a ________, is a group of species consisting of all
descendents of the group’s most recent common ancestor.
2. The three domains of life are the ________, ________, and ________.
3. The movement of genes between species is called ____________.
4. In a cladogram, an _________ is a monophyletic group in which we are interested.
5. According to the modern cladogram of eukaryotes, both fungi and animals belong to the
Opisthokonta _________.
6. In the cladistic approach, shared derived characters are also termed ________.
7. The UPGMA method provides a relatively simple method to construct a tree using the
phenetics approach. UPGMA stands for ________.
27.3 Molecular Evolution and Molecular Clocks
Overview
Molecular evolution refers to patterns and processes associated with evolutionary change
at the molecular level. This section begins by addressing the topic of homologous genes.
Familiarize yourself with the concepts of orthologs and paralogs (Figures 27.11 and 27.12). The
discussion then turns to the neutral theory of evolution (page 696). This theory suggests that most
variation in gene sequences is due to mutations that are neutral or nearly neutral with regard to
the phenotype. These variations accumulate in populations mainly due to genetic drift. Indeed,
they do so at a relatively constant rate, which can act as a molecular clock on which evolutionary
time can be measured (Figure 27.13). The section ends by highlighting how evolution also
involved changes in chromosome structure and number (Figures 27.14 and 27.15).
Outline of Key Terms
Nonneutral mutation
Neutral theory of evolution
Molecular clock
Synteny groups
Molecular evolution
Homologous genes
Orthologs
Paralogs
Gene family
Focal Points





The concept of orthologs and paralogs (Figures 27.11 and 27.12)
The neutral theory of evolution (page 696)
The concept of molecular clock (Figure 27.13)
Comparison of chromosome banding patterns among humans and apes (Figure 27.14)
Synteny groups in cereal grasses (Figure 27.15)
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Exercises and Problems
Complete the following sentences with the most appropriate word or phrase:
1. The constant rate of molecular evolutionary change can be measured by the ________.
2. Homologous genes found in different species are termed _________.
3. Homologous genes found in the same species are termed _________.
4. A ________ mutation is one that affects the phenotype of an organism and thus can be acted
on by natural selection.
5. The ________ of evolution has also been called the “survival of the luckiest”.
6. ________ mutations have a minimal effect on the phenotype—they may be slightly beneficial
or slightly detrimental.
7. ________ groups are chromosomal regions of two or more different species that contain the
same groups of linked genes.
8. In comparison to ________, human chromosome number ________ is formed by a fusion of
two smaller chromosomes, while human chromosome number ______ lacks a large _______
that flipped the arrangement of bands in the centromeric region.
27.4 Evo-Devo: Evolutionary Developmental Biology
Overview
The last section of the chapter (and the textbook) introduces a relatively new field of
biology called evolutionary developmental biology – or evo-devo for short. The aim of this field
is to compare the development of different species to understand the genes and mechanisms that
bring about evolutionary change. The discussion focuses on the key roles that genes have played
in the evolution of: 1) bird foot morphology (the BMP4 and gremlin genes); 2) animal body plan
(Hox gene cluster); and 3) eyes (Pax6 gene).
Outline of Key Terms
Evolutionary developmental biology
Evo-devo
Focal Points



The role of cell-signaling proteins in the morphology of birds’ feet (Figure 27.16)
Hox gene composition in different types of animals (Figure 27.17)
Eye evolution (Figure 27.19)
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Exercises and Problems
Complete the following sentences with the most appropriate word or phrase:
1. In birds’ feet, the protein _______ causes programmed cell death.
2. In birds’s feet, the protein ________ inhibits programmed cell death.
3. Evolution of animal body plans is related to changes in _____ gene number and expression.
4. The ______ explosion, which occurred from 533 to 525 million years ago, saw a phenomenal
diversification in the body plan of invertebrate species.
5. In humans, a mutation in the Pax6 gene results in an eye (iris) disorder called _________.
6. The ______ gene of Drosophila is homologous to the Pax6 gene of humans.
7. The field of evolutionary developmental biology is informally referred to as __________.
Chapter Quiz
1. The most prevalent model of speciation is believed to be _______ speciation.
a. sympatric
b. parapatric
c. horizontal
d. allopatric
2. A mutation that does not affect the phenotype of the individual is called a _______ mutation.
a. stabilizing
b. selective
c. neutral
d. nonsense
3. Which of the following is NOT a domain of life?
a. Bacteria
b. Animalia
c. Archaea
d. Eukarya
e. all of the above are domains
4. Hybrid zones are associated with which of the following?
a. sympatric speciation
b. parapatric speciation
c. allopatric speciation
d. artificial selection
5. Which of the following is a method used to construct phylogenetic trees?
a. Phenetics
b. Cladistics
c. Both A and B
d. Neither A nor B
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6. Which of the following are methods used to discriminate among possible phylogenetic trees?
a. maximum likelihood
b. Bayesian methods
c. principle of parsimony
d. A and B
e. A, B, and C
7. Which of the following statements about horizontal gene transfer is FALSE?
a. explains origin of mitochondria
b. explains origin of chloroplasts
c. was prevalent during early stages of evolution when all organisms were unicellular
d. continues to be a prominent factor in the speciation of eukaryotes
e. Choose this answer if all of the above are true
8. The anatomical structures of genitalia prevent mating between species. This is an example of
what isolating mechanism?
a. mechanical isolation
b. sexual isolation
c. gametic isolation
d. hybrid sterility
e. hybrid breakdown
9. In the interdigit regions in ducks, the ______ protein inhibits BMP4, thus causing webbed feet.
a. Pax6
b. Hox
c. Gremlin
d. Goblin
e. Calmodulin
10. Which of the following are example of species concepts?
a. evolutionary lineage concept
b. biological species concept
c. ecological species concept
d. A and B
e. A, B, and C
Answer Key for Study Guide Questions
This answer key provides the answers to the exercises and chapter quiz for this chapter. Answers
in parentheses ( ) represent possible alternate answers to a problem, while answers marked with
an asterisk (*) indicate that the response to the question may vary.
27.1
7. c
8. a
9. b
10. b
11. c
12. a
1. d
2. b
3. e
4. f
5. a
6. c
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27.2
1. clade
2. Archaea, Bacteria, Eukarya (Eukaryotes)
3. horizontal gene transfer
4. ingroup
5. supergroup
6. synapomorphy
7. unweighted pair group method with arithmetic mean
27.3
1. molecular clock
2. orthologs
3. paralogs
4. nonneutral
5. neutral theory
6. Nearly neutral
7. Synteny
8. orangutans; 2; 3 ; inversion
27.4
1. BMP4
2. Gremlin
3. Hox
4. Cambrian
5. aniridia
6. eyeless
7. evo-devo
Quiz
1. d
2. c
3. b
4. b
5. c
6. e
7. d
8. a
9. c
10. e
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