Genetics, analysis principles 4th ed r brooker (mcgraw hill, 2012) 1

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GENETICS: ANALYSIS & PRINCIPLES, FOURTH EDITION

Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New
York, NY 10020. Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved. Previous editions © 2009,
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limited to, in any network or other electronic storage or transmission, or broadcast for distance learning.
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This book is printed on acid-free paper.

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Library of Congress Cataloging-in-Publication Data
Brooker, Robert J.
Genetics : analysis & principles / Robert J. Brooker. — 4th ed.
p. cm.
Includes index.
ISBN 978–0–07–352528–0 — ISBN 0–07–352528–6 (hard copy : alk. paper) 1. Genetics. I. Title.
QH430.B766 2012
576.5--dc22
2010015380

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B R I E F

C O N T E N T S

::
PA R T I V MOLECULAR PROPERTIES

PA R T I INTRODUCTION
1

Overview of Genetics

OF GENES

1

PA R T I I PATTERNS OF INHERITANCE
2

Mendelian Inheritance

17

3

Reproduction and Chromosome
Transmission 44

4

Extensions of Mendelian Inheritance

5

Non-Mendelian Inheritance

6

Genetic Linkage and Mapping in
Eukaryotes 126

7

Genetic Transfer and Mapping in Bacteria
and Bacteriophages 160

8

71

100

12

Gene Transcription and RNA Modification

13

Translation of mRNA

14

Gene Regulation in Bacteria
and Bacteriophages 359

15

Gene Regulation in Eukaryotes

16

Gene Mutation and DNA Repair

17

Recombination and Transposition
at the Molecular Level 457

326

390
424

PA R T V GENETIC TECHNOLOGIES
18

Recombinant DNA Technology

Variation in Chromosome Structure
and Number 189

19

Biotechnology

20

Genomics I: Analysis of DNA

PA R T I I I MOLECULAR STRUCTURE AND

21

Genomics II: Functional Genomics, Proteomics,
and Bioinformatics 574

REPLICATION OF THE GENETIC
MATERIAL

9

Molecular Structure of DNA and RNA

10

Chromosome Organization and Molecular
Structure 247

11

299

DNA Replication

270

484

518
544

PA R T V I GENETIC ANALYSIS

222

OF INDIVIDUALS AND
POPULATIONS

22

Medical Genetics and Cancer

23

Developmental Genetics

24

Population Genetics

25

Quantitative Genetics

700

26

Evolutionary Genetics

730

602

637

670

iii

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TA B L E

O F

C O N T E N T S

::
Preface

vii

A Visual Guide to Genetics: Analysis &
Principles xiv

1
1.1
1.2

PA R T I

4.1

INTRODUCTION

4.2

OVERVIEW OF GENETICS

1

The Relationship Between Genes
and Traits 4
Fields of Genetics 10

PATTERNS OF INHERITANCE

2.1

MENDELIAN INHERITANCE

Mendel’s Laws of Inheritance

17

3
3.1
3.2
3.3
3.4

Probability and Statistics

18

General Features of
Chromosomes 44
Cell Division 48
Sexual Reproduction 54
The Chromosome Theory
of Inheritance and Sex
Chromosomes 60
Experiment 3A Morgan’s Experiments
Showed a Connection Between a

Genetic Trait and the Inheritance of a
Sex Chromosome in Drosophila 64

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NON-MENDELIAN
INHERITANCE 100

5.1
5.2

Maternal Effect 100
Epigenetic Inheritance

5.3

7.2

8
8.1

Intragenic Mapping in
Bacteriophages 176

VARIATION IN CHROMOSOME
STRUCTURE AND NUMBER 189

Variation in Chromosome
Structure 189
Experiment 8A Comparative

Genomic Hybridization Is Used to
Detect Chromosome Deletions and
Duplications 195

8.2
103

Experiment 5A In Adult Female
Mammals, One X Chromosome Has
Been Permanently Inactivated 105

Extranuclear Inheritance

8.3

Variation in Chromosome
Number 203
Natural and Experimental Ways to
Produce Variations in Chromosome
Number 208

113

PA R T I I I

6

GENETIC LINKAGE AND MAPPING
IN EUKARYOTES 126

6.1

Linkage and Crossing Over

126

Experiment 6A Creighton and
McClintock Showed That Crossing
Over Produced New Combinations of
Alleles and Resulted in the Exchange
of Segments Between Homologous
Chromosomes 133

30

REPRODUCTION
AND CHROMOSOME
TRANSMISSION 44

iv

Inheritance Patterns
of Single Genes 71
Gene Interactions 86

5
17

Experiment 2A Mendel Followed the
Outcome of a Single Character for Two

Generations 21
Experiment 2B Mendel Also Analyzed
Crosses Involving Two Different
Characters 25

2.2

EXTENSIONS OF MENDELIAN
INHERITANCE 71

Experiment 4A Bridges Observed an
8:4:3:1 Ratio Because the Cream-Eye
Gene Can Modify the X-Linked Eosin
Allele But Not the Red or
White Alleles 89

PA R T I I

2

4

Experiment 7A Conjugation
Experiments Can Map Genes Along
the E. coli Chromosome 167

6.2

6.4

7
7.1

9
9.1

MOLECULAR STRUCTURE OF DNA
AND RNA 222

Identification of DNA as the Genetic
Material 222
Experiment 9A Hershey and Chase
Provided Evidence That DNA Is the
Genetic Material of T2 Phage 225

Genetic Mapping in Plants
and Animals 136
Experiment 6B Alfred Sturtevant Used
the Frequency of Crossing Over in
Dihybrid Crosses to Produce the First
Genetic Map 138

6.3

MOLECULAR STRUCTURE AND
REPLICATION OF THE GENETIC
MATERIAL 222

9.2

Nucleic Acid Structure

Genetic Mapping in Haploid
Eukaryotes 143
Mitotic Recombination 149

GENETIC TRANSFER AND
MAPPING IN BACTERIA AND
BACTERIOPHAGES 160

Genetic Transfer and Mapping
in Bacteria 161

229

Experiment 9B Chargaff Found That
DNA Has a Biochemical Composition in
Which the Amount of A Equals T and
the Amount of G Equals C 232

10

CHROMOSOME
ORGANIZATION
AND MOLECULAR
STRUCTURE 247

10.1 Viral Genomes 247
10.2 Bacterial Chromosomes

249

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v

TABLE OF CONTENTS

10.3 Eukaryotic Chromosomes

252

Experiment 10A The Repeating
Nucleosome Structure Is Revealed by
Digestion of the Linker Region 257

11

DNA REPLICATION

270

11.1 Structural Overview of DNA
Replication 270
Experiment 11A Three Different Models
Were Proposed That Described the Net
Result of DNA Replication 272

11.2 Bacterial DNA Replication

14.2 Translational and Posttranslational
Regulation 375
14.3 Riboswitches 377
14.4 Gene Regulation in the Bacteriophage
Reproductive Cycle 378

274

Experiment 11B DNA Replication Can
Be Studied in Vitro 285

11.3 Eukaryotic DNA Replication

288

15

Experiment 15A Fire and Mello Show
That Double-Stranded RNA Is More
Potent Than Antisense RNA at Silencing
mRNA 411

MOLECULAR PROPERTIES
OF GENES 299

12
12.1
12.2
12.3

12.4

GENE TRANSCRIPTION AND
RNA MODIFICATION 299

Overview of Transcription 300
Transcription in Bacteria 302
Transcription in Eukaryotes 307
RNA Modification 310

16

326

13.1 The Genetic Basis for Protein
Synthesis 326
Experiment 13A Synthetic RNA Helped
to Decipher the Genetic Code 332

13.2 Structure and Function of tRNA

340

Experiment 13B tRNA Functions as the
Adaptor Molecule Involved in Codon
Recognition 340

GENE REGULATION
IN BACTERIA AND
BACTERIOPHAGES 359

14.1 Transcriptional Regulation

360

Experiment 14A The lacI Gene Encodes
a Diffusible Repressor Protein 365

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425

17

RECOMBINATION AND
TRANSPOSITION AT THE
MOLECULAR LEVEL 457

17.1 Homologous Recombination

RECOMBINANT DNA
TECHNOLOGY 484

Experiment 18A Early Attempts at
Monitoring the Course of PCR Used
Ethidium Bromide as a Detector 498

18.3 DNA Libraries and Blotting
Methods 499
18.4 Methods for Analyzing DNA- and RNABinding Proteins 505

18.5 DNA Sequencing and Site-Directed
Mutagenesis 507

19

457

Experiment 17A The Staining of
Harlequin Chromosomes Can Reveal
Recombination Between Sister
Chromatids 458

518

Experiment 19A Adenosine Deaminase
Deficiency Was the First Inherited Disease
Treated with Gene Therapy 538
GENOMICS I: ANALYSIS
OF DNA 544

20.1 Overview of Chromosome Mapping 545
20.2 Cytogenetic Mapping Via
Microscopy 545
20.3 Linkage Mapping Via Crosses 547
20.4 Physical Mapping Via Cloning 553
20.5 Genome-Sequencing Projects 559
Experiment 20A Venter, Smith, and
Colleagues Sequenced the First
Genome in 1995 559

466

Experiment 17B McClintock Found That
Chromosomes of Corn Plants Contain
Loci That Can Move 468

BIOTECHNOLOGY

19.1 Uses of Microorganisms
in Biotechnology 518
19.2 Genetically Modified Animals 522
19.3 Reproductive Cloning and Stem
Cells 527
19.4 Genetically Modified Plants 532
19.5 Human Gene Therapy 536

20

443

17.2 Site-Specific Recombination
17.3 Transposition 468

13.3 Ribosome Structure and
Assembly 345
13.4 Stages of Translation 347

14

18

Experiment 16A X-Rays Were the First
Environmental Agent Shown to Cause
Induced Mutations 439

16.3 DNA Repair
TRANSLATION OF mRNA

424

16.1 Consequences of Mutation
16.2 Occurrence and Causes of
Mutation 431

Experiment 12A Introns Were
Experimentally Identified via
Microscopy 313

13

GENE MUTATION
AND DNA REPAIR

GENETIC TECHNOLOGIES 484

18.1 Gene Cloning Using Vectors 485
18.2 Polymerase Chain Reaction 491

GENE REGULATION IN
EUKARYOTES 390

15.1 Regulatory Transcription Factors 391
15.2 Chromatin Remodeling,
Histone Variation, and Histone
Modification 397
15.3 DNA Methylation 403
15.4 Insulators 406
15.5 Regulation of RNA Processing, RNA
Stability, and Translation 407

PA R T I V

PA R T V

21

GENOMICS II: FUNCTIONAL
GENOMICS, PROTEOMICS,
AND BIOINFORMATICS 574

21.1 Functional Genomics

575

Experiment 21A The Coordinate
Regulation of Many Genes Is Revealed
by a DNA Microarray Analysis 577

21.2 Proteomics 583
21.3 Bioinformatics 587

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vi

TA B L E O F C O N T E N T S

PA R T V I
GENETIC ANALYSIS
OF INDIVIDUALS AND
POPULATIONS 602

22

24

MEDICAL GENETICS
AND CANCER 602

22.1 Inheritance Patterns of Genetic
Diseases 603
22.2 Detection of Disease-Causing
Alleles 609
22.3 Prions 613
22.4 Genetic Basis of Cancer 614
Experiment 22A DNA Isolated from
Malignant Mouse Cells Can Transform
Normal Mouse Cells into Malignant
Cells 616

23

DEVELOPMENTAL
GENETICS 637

23.1 Overview of Animal
Development 637
23.2 Invertebrate Development

26

23.3 Vertebrate Development 652
23.4 Plant Development 656
23.5 Sex Determination in Animals
and Plants 659

POPULATION GENETICS

26.1 Origin of Species 731
26.2 Phylogenetic Trees 738
26.3 Molecular Evolution 744
670

24.1 Genes in Populations and the
Hardy-Weinberg Equation 670
24.2 Factors That Change Allele
and Genotype Frequencies in
Populations 675
Experiment 24A The Grants Have

Observed Natural Selection in
Galápagos Finches 686

24.3 Sources of New Genetic
Variation 689

25

QUANTITATIVE
GENETICS 700

25.1 Quantitative Traits 700
25.2 Polygenic Inheritance 705
640

Experiment 23A Heterochronic
Mutations Disrupt the Timing of
Developmental Changes
in C. elegans 650

EVOLUTIONARY
GENETICS 730

Experiment 26A Scientists Can
Analyze Ancient DNA to Examine the
Relationships Between Living and
Extinct Flightless Birds 748

26.4 Evo-Devo: Evolutionary Developmental
Biology 753

Appendix A
Experimental Techniques A-1
Appendix B
Solutions to Even-Numbered
Problems A-8
Glossary G-1
Credits C-1
Index I-1

Experiment 25A Polygenic Inheritance
Explains DDT Resistance
in Drosophila 708

25.3 Heritability

711

Experiment 25B Heritability of Dermal
Ridge Count in Human Fingerprints
Is Very High 716

ABOUT THE AUTHOR
Robert J. Brooker is a professor in the Department of
Genetics, Cell Biology, and Development at the University of
Minnesota–Minneapolis. He received his B.A. in biology from
Wittenberg University in 1978 and his Ph.D. in genetics from
Yale University in 1983. At Harvard, he conducted postdoctoral
studies on the lactose permease, which is the product of the lacY
gene of the lac operon. He continues his work on transporters at
the University of Minnesota. Dr. Brooker’s laboratory primarily

investigates the structure, function, and regulation of iron
transporters found in bacteria and C. elegans. At the University of
Minnesota he teaches undergraduate courses in biology, genetics,
and cell biology.

DEDICATION
To my wife, Deborah, and our children, Daniel, Nathan, and Sarah

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P R E FA C E

::

I

n the fourth edition of Genetics: Analysis & Principles, the
content has been updated to reflect current trends in the field. In
addition, the presentation of the content has been improved in
a way that fosters active learning. As an author, researcher, and
teacher, I want a textbook that gets students actively involved
in learning genetics. To achieve this goal, I have worked with a
talented team of editors, illustrators, and media specialists who
have helped me to make the fourth edition of Genetics: Analysis & Principles a fun learning tool. The features that we feel are
most appealing to students, and which have been added to or
improved on in the fourth edition, are the following.
• Interactive exercises Education specialists have crafted

interactive exercises in which the students can make their
own choices in problem-solving activities and predict what
the outcomes will be. Previously, these exercises focused
on inheritance patterns and human genetic diseases. (For
example, see Chapters 4 and 22.) For the fourth edition,
we have also added many new interactive exercises for the
molecular chapters.
• Animations Our media specialists have created over
50 animations for a variety of genetic processes. These
animations were made specifically for this textbook and use
the art from the textbook. The animations make many of
the figures in the textbook “come to life.”
• Experiments As in the previous editions, each chapter
(beginning with Chapter 2) incorporates one or two experiments that are presented according to the scientific method.
These experiments are not “boxed off ” from the rest of
the chapter. Rather, they are integrated within the chapters
and flow with the rest of the text. As you are reading the
experiments, you will simultaneously explore the scientific
method and the genetic principles that have been discovered
using this approach. For students, I hope this textbook helps
you to see the fundamental connection between scientific
analysis and principles. For both students and instructors, I
expect that this strategy makes genetics much more fun to
explore.
• Art The art has been further refined for clarity and completeness. This makes it easier and more fun for students to
study the illustrations without having to go back and forth
between the art and the text.
• Engaging text As in previous editions, a strong effort has
been made in the fourth edition to pepper the text with
questions. Sometimes these are questions that scientists

considered when they were conducting their research.

Red
P generation

White

CRCR

CWCW

x

Gametes CR

CW

Pink
F1 generation
CRCW

Gametes CR or CW
Self-fertilization

Sperm
F2 generation

CR

CW

CRCR

CRCW

CRCW

CWCW

CR
Egg
CW

F IG U R E 4 . 3 Incomplete dominance in the
four-o’clock plant, Mirabilis jalapa.
Genes → Traits When two different homozygotes (C RC R and
C WC W) are crossed, the resulting heterozygote, C RC W, has an intermediate phenotype
of pink flowers. In this case, 50% of the functional protein encoded by the C R allele
is not sufficient to produce a red phenotype.

Sometimes they are questions that the students might ask
themselves when they are learning about genetics.
Overall, an effective textbook needs to accomplish three
goals. First, it needs to provide comprehensive, accurate, and upto-date content in its field. Second, it needs to expose students to
the techniques and skills they will need to become successful in
vii

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viii

P R E FA C E

that field. And finally, it should inspire students so they want to
pursue that field as a career. The hard work that has gone into the
fourth edition of Genetics: Analysis & Principles has been aimed at
achieving all three of these goals.

HOW WE EVALUATED YOUR NEEDS
ORGANIZATION
In surveying many genetics instructors, it became apparent that
most people fall into two camps: Mendel first versus Molecular
first. I have taught genetics both ways. As a teaching tool, this
textbook has been written with these different teaching strategies
in mind. The organization and content lend themselves to various teaching formats.
Chapters 2 through 8 are largely inheritance chapters,
whereas Chapters 24 through 26 examine population and quantitative genetics. The bulk of the molecular genetics is found in Chapters 9 through 23, although I have tried to weave a fair amount of
molecular genetics into Chapters 2 through 8 as well. The information in Chapters 9 through 23 does not assume that a student
has already covered Chapters 2 through 8. Actually, each chapter
is written with the perspective that instructors may want to vary
the order of their chapters to fit their students’ needs.
For those who like to discuss inheritance patterns first, a
common strategy would be to cover Chapters 1 through 8 first,
and then possibly 24 through 26. (However, many instructors like to cover quantitative and population genetics at the
end. Either way works fine.) The more molecular and technical
aspects of genetics would then be covered in Chapters 9 through
23. Alternatively, if you like the “Molecular first” approach, you

would probably cover Chapter 1, then skip to Chapters 9 through
23, then return to Chapters 2 through 8, and then cover Chapters
24 through 26 at the end of the course. This textbook was written
in such a way that either strategy works well.

ACCURACY
Both the publisher and I acknowledge the fact that inaccuracies
can be a source of frustration for both the instructor and students. Therefore, throughout the writing and production of this
textbook we have worked very hard to catch and correct errors
during each phase of development and production.
Each chapter has been reviewed by a minimum of seven
people. At least five of these people were faculty members who
teach the course or conduct research in genetics or both. In
addition, a development editor has gone through the material
to check for accuracy in art and consistency between the text
and art. With regard to the problem sets, the author personally
checked every question and answer when the chapters were completed.

PEDAGOGY
Based on our discussions with instructors from many institutions, some common goals have emerged. Instructors want a

bro25286_FM.indd viii

broad textbook that clearly explains concepts in a way that is
interesting, accurate, concise, and up-to-date. Likewise, most
instructors want students to understand the experimentation
that revealed these genetic concepts. In this textbook, concepts
and experimentation are woven together to provide a story that
enables students to learn the important genetic concepts that they
will need in their future careers and also to be able to explain the

types of experiments that allowed researchers to derive such concepts. The end-of-chapter problem sets are categorized according
to their main focus, either conceptual or experimental, although
some problems contain a little of both. The problems are meant
to strengthen students’ abilities in a wide variety of ways.
• By bolstering their understanding of genetic principles
• By enabling students to apply genetic concepts to new
situations
• By analyzing scientific data
• By organizing their thoughts regarding a genetic topic
• By improving their writing skills
Finally, since genetics is such a broad discipline, ranging
from the molecular to the populational levels, many instructors have told us that it is a challenge for students to see both
“the forest and the trees.” It is commonly mentioned that students often have trouble connecting the concepts they have
learned in molecular genetics with the traits that occur at the
level of a whole organism (i.e., What does transcription have
to do with blue eyes?). To try to make this connection more
meaningful, certain figure legends in each chapter, designated
Genes → Traits, remind students that molecular and cellular
phenomena ultimately lead to the traits that are observed in each
species (e.g., see Figure 4.3).

ILLUSTRATIONS
In surveying students whom I teach, I often hear it said that
most of their learning comes from studying the figures. Likewise,
instructors frequently use the illustrations from a textbook as a
central teaching tool. For these reasons, a great amount of effort
in improving the fourth edition has gone into the illustrations.
The illustrations are created with four goals in mind:
1. Completeness For most figures, it should be possible to
understand an experiment or genetic concept by looking at

the illustration alone. Students have complained that it is
difficult to understand the content of an illustration if they
have to keep switching back and forth between the figure
and text. In cases where an illustration shows the steps in a
scientific process, the steps are described in brief statements
that allow the students to understand the whole process
(e.g., see Figure 11.16). Likewise, such illustrations should
make it easier for instructors to explain these processes in
the classroom.
2. Clarity The figures have been extensively reviewed
by students and instructors. This has helped us to avoid
drawing things that may be confusing or unclear. I hope

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ix

PREFACE

that no one looks at an element in any figure and wonders,
“What is that thing?” Aside from being unmistakably drawn,
all new elements within each figure are clearly labeled.
3. Consistency Before we began to draw the figures for the
fourth edition, we generated a style sheet that contained
recurring elements that are found in many places in the
textbook. Examples include the DNA double helix, DNA
polymerase, and fruit flies. We agreed on the best way(s) to
draw these elements and also what colors they should be.
Therefore, as students and instructors progress through this

textbook, they become accustomed to the way things should
look.
4. Realism An important goal of this and previous editions
is to make each figure as realistic as possible. When
drawing macroscopic elements (e.g., fruit flies, pea plants),
the illustrations are based on real images, not on cartoonlike
simplifications. Our most challenging goal, and one that we
feel has been achieved most successfully, is the realism of our
molecular drawings. Whenever possible, we have tried to
depict molecular elements according to their actual structures,
if such structures are known. For example, the ways we have
drawn RNA polymerase, DNA polymerase, DNA helicase,
and ribosomes are based on their crystal structures. When a
student sees a figure in this textbook that illustrates an event,
for example proofreading DNA, DNA polymerase is depicted
in a way that is as realistic as possible (e.g., see Figure 11.16).

Mismatch causes DNA polymerase to pause,
leaving mismatched nucleotide near the 3′ end.

3′ exonuclease
site

T
3′

Template
strand
5′

C
5′

Base pair
mismatch
near the
3′ end

3′

The 3′ end enters the
exonuclease site.

3′
3′
5′

5′

WRITING STYLE
Motivation in learning often stems from enjoyment. If you enjoy
what you’re reading, you are more likely to spend longer amounts
of time with it and focus your attention more crisply. The writing
style of this book is meant to be interesting, down to earth, and
easy to follow. Each section of every chapter begins with an overview of the contents of that section, usually with a table or figure
that summarizes the broad points. The section then examines
how those broad points were discovered experimentally, as well
as explaining many of the finer scientific details. Important terms
are introduced in a boldface font. These terms are also found in
the glossary.

There are various ways to make a genetics book interesting and inspiring. The subject matter itself is pretty amazing, so
it’s not difficult to build on that. In addition to describing the
concepts and experiments in ways that motivate students, it is
important to draw on examples that bring the concepts to life.
In a genetics book, many of these examples come from the medical realm. This textbook contains lots of examples of human diseases that exemplify some of the underlying principles of genetics. Students often say they remember certain genetic concepts
because they remember how defects in certain genes can cause
disease. For example, defects in DNA repair genes cause a higher
predisposition to develop cancer. In addition, I have tried to be
evenhanded in providing examples from the microbial and plant
world. Finally, students are often interested in applications of
genetics that affect their everyday lives. Because we frequently

bro25286_FM.indd ix

At the 3′ exonuclease site,
the strand is digested in
the 3′ to 5′ direction until the
incorrect nucleotide is
removed.

Incorrect
nucleotide
removed
3′

5′

5′

F I G U R E 1 1 . 1 6 The proofreading function of

DNA polymerase. When a base pair mismatch is found,
the end of the newly made strand is shifted into the 3ʹ
exonuclease site. The DNA is digested in the 3ʹ to 5ʹ
direction to release the incorrect nucleotide.
hear about genetics in the news, it’s inspiring for students to
learn the underlying basis for such technologies. Chapters 18 to
21 are devoted to genetic technologies, and applications of these

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x

P R E FA C E

and other technologies are found throughout this textbook. By
the end of their genetics course, students should come away with
a greater appreciation for the influence of genetics in their lives.

SIGNIFICANT CONTENT CHANGES
IN THE FOURTH EDITION
• A new feature of the fourth edition is that each chapter ends
with a list of key terms. These are the terms in the chapter
that are in bold face. The terms are also found in the
glossary. This addition was made at the request of students.
• The summary at the end of the chapter has been modified
in two ways. First, the key points are found as bulleted lists.
Second, the bulleted lists also refer to the figures and tables
where the topics can be found. This modification was made
at the request of students, who said that it was difficult to

easily extract the main points from summaries that were in
paragraph form, as they were in previous editions.
• The chapter on Non-Mendelian Inheritance (formerly
Chapter 7) is now Chapter 5. This change was made at
the request of instructors who often cover the chapters on
Mendelian and Non-Mendelian inheritance consecutively.

Examples of Specific Content Changes to
Individual Chapters
• Chapter 2 (Mendelian Inheritance) An improved figure
on Mendel's law of segregation has been added (Figure 2.6).
• Chapter 3 (Reproduction and Chromosome
Transmission) An improved figure emphasizes how
chromosomes in a karyotype are pairs of sister chromatids
(see Figure 3.6). Also, the stages of mitosis and meiosis
are set off as subsections with bold headings, which makes
them easier to follow.
• Chapter 5 (Non-Mendelian Inheritance) Information
regarding the molecular mechanism of imprinting has been
updated, including a descripiton of CTC-binding factor.
With regard to human mitochondrial diseases, the topics of
heteroplasmy and somatic mutation have been expanded.
• Chapter 6 (Genetic and Linkage Mapping in Eukaryotes)
A new figure illustrates the outcome of crossing over
between two linked genes in Morgan's classic experiments
(see Figure 6.4). This is then followed up with another
figure that shows the consequences of crossing over among
three linked genes (see Figure 6.5).
• Chapter 7 (Genetic Transfer and Mapping in Bacteria
and Bacteriophages) A new figure depicts how F' factors

arise by the imprecise excision of F factors from a
chromosome (see Figure 7.5b).
• Chapter 8 (Variation in Chromosome Structure and
Number) New information and figures have been added
regarding nonallelic homologous recombination and copy
number variation in populations (see Figures 8.5 and 8.8).
• Chapter 10 (Chromosome Organization and Molecular
Structure) New figures have been added on the action
of DNA gyrase and the relative amounts of unique and

bro25286_FM.indd x

•

•

•

•

•

•

•

•

•
•

•

•

repetitive sequences in the human genome (see Figures 10.9
and 10.12).
Chapter 11 (DNA Replication) A new figure illustrates
DNA replication from a single origin (see Figure 11.11).
Also, the topic of how RNA primers are removed by flap
endonuclease in eukaryotic cells has been added, which
includes a new figure (see Figure 11.23).
Chapter 12 (Gene Transcription and RNA Modification)
The mechanism of transcriptional termination in eukaryotes
via the allosteric or torpedo models has been added (see
Figure 12.15). Also, RNA editing has been moved to this
chapter.
Chapter 13 (Translation of mRNA) A new figure describes
Beadle and Tatum's study of methionine biosynthesis
(see Figure 13.2). The topic of the incorporation of
selenocysteine and pyrrolysine during translation has been
added (see Table 13.3).
Chapter 14 (Gene Regulation in Bacteria and
Bacteriophages) This chapter has a new section on
riboswitches (see pp. 377–378).
Chapter 15 (Gene Regulation in Eukaryotes) A new
section has been added on chromatin remodeling, histone
variation, and histone modification (see pp. 397–403).
A new figure describes the technique of chromatin
immunoprecipitation sequencing (see Figure 15.11). A new

section has been added on insulators (see pp. 406–407).
Chapter 16 (Gene Mutation and DNA Repair) The topic
of oxidative stress and oxidative DNA damage has been
greatly expanded (see pp. 435–437). A new figure depicts
the probable mechanism of trinucleotide repeat expansion
(see Figure 16.12).
Chapter 17 (Recombination and Transposition at the
Molecular Level) A new figure describes the transposition
of non-LTR retrotransposons (see Figure 17.18).
Chapter 18 (Recombinant DNA Technology) The topic
of polymerase chain reaction (PCR) is now expanded to
an entire section, which includes several new figures that
describe the steps of the PCR cycle, reverse transcriptase
PCR, real-time PCR, and the classic experiment that
demonstrated the feasibility of real-time PCR (see pp. 491–
499).
Chapter 19 (Biotechnology) A new feature experiment
describes the method of gene therapy (see Figure 19.20).
Chapter 20 (Genomics I: Analysis of DNA) A
new subsection has been added on next-generation
DNA sequencing methods, including a new figure on
pyrosequencing (see pp. 564–566).
Chapter 21 (Genomics II: Functional Genomics,
Proteomics, and Bioinformatics) A new subsection has been
added that discusses gene knockout collections.
Chapter 22 (Medical Genetics and Cancer) Two new
subsections have been added on haplotypes and haplotype
association studies (see pp. 609–610, Figures 22.5–22.6).
The topic of preimplantation genetic diagnosis has also
been added. With regard to inherited forms of cancer, a new

figure describes how the "loss of heterozygosity" leads to
cancer (see Figure 22.22).

12/6/10 12:57 PM


PREFACE

• Chapter 23 (Developmental Genetics) A new section has
been added at the beginning of the chapter that provides
a general overview of animal development (see pp. 638–
641). This precedes the two sections on Invertebrate and
Vertebrate Development.
• Chapter 24 (Population Genetics) A new figure shows
the output from automated DNA fingerprinting (see Figure
24.22).
• Chapter 26 (Evolutionary Genetics) The topic of species
concepts is more focused on the factors that are used to
distinguish species; the general lineage concept is described
(see pp. 734–736). A new example illustrates the concept of
a molecular clock (see Figure 26.14).

xi

ConnectPlus™ Genetics provides students with all the
advantages of Connect™ Genetics, plus 24/7 online access to an
eBook.

SUGGESTIONS WELCOME!
It seems very appropriate to use the word evolution to describe

the continued development of this textbook. I welcome any and
all comments. The refinement of any science textbook requires
input from instructors and their students. These include comments regarding writing, illustrations, supplements, factual content, and topics that may need greater or less emphasis. You are
invited to contact me at:
Dr. Rob Brooker
Dept. of Genetics, Cell Biology, and Development
University of Minnesota
6-160 Jackson Hall
321 Church St.
Minneapolis, MN 55455


TEACHING AND LEARNING
SUPPLEMENTS

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bro25286_FM.indd xi

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12/6/10 12:57 PM


xii

P R E FA C E

FOR THE STUDENT:
Student Study Guide/Solutions Manual
The solutions to the end-of-chapter problems and questions
aid the students in developing their problem-solving skills by
providing the steps for each solution. The Study Guide follows the
order of sections and subsections in the textbook and summarizes
the main points in the text, figures, and tables. It also contains
concept-building exercises, self-help quizzes, and practice exams.
Companion Website
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The Brooker Genetics: Analysis & Principles companion website
offers an extensive array of learning tools, including a variety of
quizzes for each chapter, interactive genetics problems, animations
and more.

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ACKNOWLEDGMENTS
The production of a textbook is truly a collaborative effort,
and I am greatly indebted to a variety of people. All four editions of this textbook went through multiple rounds of rigorous
revision that involved the input of faculty, students, editors, and
educational and media specialists. Their collective contributions
are reflected in the final outcome.
Let me begin by acknowledging the many people at
McGraw-Hill whose efforts are amazing. My highest praise goes
to Lisa Bruflodt and Mandy Clark (Senior Developmental Editors), who managed and scheduled nearly every aspect of this
project. I also would like to thank Janice Roerig-Blong (Publisher) for her patience in overseeing this project. She has the
unenviable job of managing the budget for the book and that is
not an easy task. Other people at McGraw-Hill have played key
roles in producing an actual book and the supplements that go
along with it. In particular, Jayne Klein (Project Manager) has
done a superb job of managing the components that need to be
assembled to produce a book, along with Sherry Kane (Buyer). I
would also like to thank John Leland (Photo Research Coordinator), who acted as an interface between me and the photo company. In addition, my gratitude goes to David Hash (Designer),
who provided much input into the internal design of the book as
well as creating an awesome cover. Finally, I would like to thank
Patrick Reidy (Marketing Manager), whose major efforts begin
when the fourth edition comes out! I would also like to thank
Linda Davoli (Freelance Copy Editor) for making grammatical
improvements throughout the text and art, which has significantly improved the text's clarity.

McGraw-Hill Higher Education and Blackboard® have teamed up.

bro25286_FM.indd xii

12/7/10 3:04 PM

PREFACE

I would also like to extend my thanks to Bonnie Briggle
and everyone at Lachina Publishing Services, including the many
artists who have played important roles in developing the art for
the third and fourth editions. Also, folks at Lachina Publishing
Services worked with great care in the paging of the book, making sure that the figures and relevant text are as close to each
other as possible. Likewise, the people at Pronk & Associates

REVIEWERS
Agnes Ayme-Southgate, College of
Charleston
Diya Banerjee, Virginia Polytechnic Institute
Miriam Barlow, University of California
Bruce Bejcek, Western Michigan University
Michael Benedik, University of Houston
Helen Chamberlin, Ohio State University
Michael Christoffers, North Dakota State
University
Craig Coleman, Brigham Young University–
Provo
Brian Condie, University of Georgia
Erin Cram, Northeastern University
Mack Crayton, Xavier University of
Louisiana
Stephen D’Surney, University of Mississippi
Sandra Davis, University of Indianapolis
Michael Deyholos, University of Alberta
Robert Dotson, Tulane University

Richard Duhrkopf, Baylor University
Aboubaker Elkharroubi, John Hopkins
University
Matthew Elrod-Erickson, Middle Tennessee
State University
Rebecca Ferrell, Metro State College of
Denver
Cedric Feschotte, The University of Texas–
Arlington
Michael Foster, Eastern Kentucky University
Gail Gasparich, Towson University
Jayant Ghiara, University of California–San
Diego
Doreen Glodowski, Rutgers University
Richard Gomulkiewicz, Washington State
University – Pullman
Ernest Hanning, The University of Texas–
Dallas
Michael Harrington, University of Alberta
Jutta Heller, Loyola University
Bethany Henderson-Dean, University of
Findlay
Brett Holland, California State University–
Sacramento
Margaret Hollingsworth, SUNY Buffalo

bro25286_FM.indd xiii

xiii

have done a great job of locating many of the photographs that
have been used in the fourth edition.
Finally, I want to thank the many scientists who reviewed
the chapters of this textbook. Their broad insights and constructive suggestions were an important factor that shaped its final content and organization. I am truly grateful for their time and effort.

Dena Johnson, Tarrant County College NW
Christopher Korey, College of Charleston
Howard Laten, Loyola University
Haiying Liang, Clemson University
Qingshun Quinn Li, Miami University
Dmitri Maslov, University of California–
Riverside
Debra McDonough, University of New
England–Biddeford
David McFadyen, Grant MacEwan College
Marcie Moehnke, Baylor University
Roderick Morgan, Grand Valley State
University
Sally Pasion, San Francisco State University
James Prince, California State University–
Fresno
Richard Richardson, University of Texas–
Austin
William Rosche, Richard Stockton College
of NJ
Mark Rovedo, Loyola University
Laurie Russell, Saint Louis University
Gwen Sancar, University of North Carolina–
Chapel Hill
Malcolm Schug, University of North

Carolina–Greensboro
Julian Kenneth Shull, Appalachian State
University
Jeffry Shultz, Louisiana Tech University
Randall Small, University of Tennessee–
Knoxville
Terrance Michael Stock, Grant MacEwan
College
Tin Tin Su, University of Colorado–Boulder
John David Swanson, University of Central
Arkansas
Daniel Yunqiu Wang, University of Miami–
Coral Gables
Qun-Tian Wang, University of Illinois–
Chicago
Matthew White, Ohio University–Athens
Malcolm Zellars, Georgia State University
Robert Zemetra, University of Idaho
Chaoyang Zeng, University of Wisconsin–
Milwaukee

ACCURACY CHECKERS
Agnes Ayme-Southgate, College of
Charleston
Diya Banerjee, Virginia Polytechnic Institute
Miriam Barlow, University of California
Bruce Bejcek, Western Michigan University
Michael Benedik, University of Houston
Helen Chamberlin, Ohio State University
Michael Christoffers, North Dakota State

University
Sandra Davis, University of Indianapolis
Michael Deyholos, University of Alberta
Aboubaker Elkharroubi, John Hopkins
University
Michael Foster, Eastern Kentucky University
Jutta Heller, Loyola University
Bethany Henderson-Dean, University of
Findlay
Margaret Hollingsworth, SUNY Buffalo
Michael Ibba, Ohio State University
Dena Johnson, Tarrant County College NW
Haiying Liang, Clemson University
Qingshun Quinn Li, Miami University
Dmitri Maslov, University of California–
Riverside
Marcie Moehnke, Baylor University
Roderick Morgan, Grand Valley State
University
Laurie Russell, Saint Louis University
Tin Tin Su, University of Colorado–Boulder
John David Swanson, University of Central
Arkansas
Matthew White, Ohio University–Athens

12/6/10 12:57 PM


A Visual Guide to
G E N E T I C S :

A N A LY S I S

&

P R I N C I P L E S

::
Instructional Art
2 nm

Key Features

5′ P 3′
S P
A S

• Two strands of DNA form a
right-handed double helix.

P

• The 2 strands are antiparallel with
regard to their 5′ to 3′ directionality.

S

P

• The bases in opposite strands

hydrogen bond according to the
AT/GC rule.

Each figure is carefully designed to follow
closely with the text material.

P

S

G

S

P
C
P S
S

G

S
C

P

• There are ~10.0 nucleotides in each P S
P
strand per complete 360° turn of
S P

the helix.
S
A T S

Isolate genomic DNA
and break into fragments.

Deposit the beads into a picotiter S C
plate. Only one bead can fit into
P
each well.

P
S

C

P

A

T
P

S

SC

G
C

S

Add sequencing
sequenci
sequ
q enci
encing
ng
g reagents:
reage
reage
eagents:
g nts:
DNA polymerase, primers,
ATP sulfurylase, luciferase,
apyrase, adenosine 5′
monophosphate, and luciferin.
Sequentially flow solutions
containing A, T, G, or C into the
wells. In the example below, T
has been added to the wells.

T

Emulsify the beads so there is only
one bead per droplet. The droplets
also contain PCR reagents that
amplify the DNA.

H H
O

H

O–

CH2 O P

O

H

CH2

NH2

C

H

O
H

H H
N

G

O

H

H2N

CH2

O

O

H

CH3

T

O

O

O

N

H2N
N

H

H

H

G S
G
P

H H
N

A

–

H

O–

CH2 O P

H

N
O

H H

H

N

N

O

N

O
H N

N

N

O

O

P

N

H H

H
O

H

H

H

O–

CH2 O P

N

H

O

O
O P

O

One nucleotide
0.34 nm

N

CH2

O–
H

G

O

H

H

OH

H

N
H

N H
NH2

H

H2 N
N

C

H

H
N

H H

H

O
H

O

O–

CH2 O P

O

O–

3′ end
S

O

O

H

S

S

5′ end

P

G

S
5′

3′

The digitally rendered images have
a vivid three-dimensional look that
will stimulate a student’s interest and
enthusiasm.

Thymine nucleotides

G

O

H

HO

H

O

H

O P

S

P S

PPi (pyrophosphate) is released
when T is incorporated into the
growing strand.

CAT

H

N

N

H

C P

P

P

Denature the DNA into single
strands and attach to beads via
the adaptors. Note: only one DNA

strand is attached to a bead.

N

H
O

H

P S
PS
P

Adaptors

A

T

O
O

N

S

A
C

H

O–

S

T
G

O

H

H

N

H

S

S

CH2

NH2

O–

T A
P

G
S
P

P

O

O–

O P

P
One complete
turn 3.4 nm

O P

N

H

O–

P

P S

Covalently attach oligonucleotide
adapters to the 5′ and 3′ ends of

the DNA.

3′ end
H

CH3

S

H

G

S

Fragment of
genomic DNA

5′ end

P

C

T

CA
T

Antennapedia

complex

Primer
PPi + Adenosine 5′
monophosphate
ATP sulfurylase

bithorax
complex

Fly
chromosome

ATP + luciferin

lab pb Dfd Scr Antp Ubx abd-A Abd-B

Luciferase
Light
Light is detected by a camera
in the sequencing machine.

Embryo
(10 hours)

Adult

Every illustration was drawn with four goals in mind:
completeness, clarity, consistency, and realism.

xiv

bro25286_FM.indd xiv

12/6/10 12:57 PM


Learning Through Experimentation
Each chapter (beginning with Chapter 2) incorporates one or two experiments that are presented according to the scientific
method. These experiments are integrated within the chapters and flow with the rest of the textbook. As you read the experiments,
you will simultaneously explore the scientific method and the genetic principles learned from this approach.
6.1 LINKAGE AND CROSSING OVER

133

EXPERIMENT 6A

STEP 1: BACKGROUND
OBSERVATIONS
Each experiment begins with a
description of the information that led
researchers to study an experimental
problem. Detailed information about
the researchers and the experimental
challenges they faced help students to
understand actual research.

Creighton and McClintock Showed That Crossing
Over Produced New Combinations of Alleles
and Resulted in the Exchange of Segments

Between Homologous Chromosomes
As we have seen, Morgan’s studies were consistent with the
hypothesis that crossing over occurs between homologous chromosomes to produce new combinations of alleles. To obtain direct
evidence that crossing over can result in genetic recombination,
Harriet Creighton and Barbara McClintock used an interesting
strategy involving parallel observations. In studies conducted in
1931, they first made crosses involving two linked genes to produce parental and recombinant offspring. Second, they used a
microscope to view the structures of the chromosomes in the parents and in the offspring. Because the parental chromosomes had
some unusual structural features, they could microscopically distinguish the two homologous chromosomes within a pair. As we
will see, this enabled them to correlate the occurrence of recombinant offspring with microscopically observable exchanges in
segments of homologous chromosomes.
Creighton and McClintock focused much of their attention
on the pattern of inheritance of traits in corn. This species has 10
different chromosomes per set, which are named chromosome 1,
chromosome 2, chromosome 3, and so on. In previous cytological examinations of corn chromosomes, some strains were found
to have an unusual chromosome 9 with a darkly staining knob at
one end. In addition, McClintock identified an abnormal version
of chromosome 9 that also had an extra piece of chromosome 8
attached at the other end (Figure 6.6a). This chromosomal rearrangement is called a translocation.
Creighton and McClintock insightfully realized that
this abnormal chromosome could be used to determine if two
homologous chromosomes physically exchange segments as a
result of crossing over. They knew that a gene was located near
the knobbed end of chromosome 9 that provided color to corn
kernels. This gene existed in two alleles, the dominant allele C
(colored) and the recessive allele c (colorless). A second gene,
located near the translocated piece from chromosome 8, affected
the texture of the kernel endosperm. The dominant allele Wx
caused starchy endosperm, and the recessive wx allele caused
waxy endosperm. Creighton and McClintock reasoned that a

crossover involving a normal chromosome 9 and a knobbed/
translocated chromosome 9 would produce a chromosome that
had either a knob or a translocation, but not both. These two
types of chromosomes would be distinctly different from either
of the parental chromosomes (Figure 6.6b).
As shown in the experiment of Figure 6.7, Creighton and
McClintock began with a corn strain that carried an abnormal
chromosome that had a knob at one end and a translocation at
the other. Genotypically, this chromosome was C wx. The cytologically normal chromosome in this strain was c Wx. This corn
plant, termed parent A, had the genotype Cc Wx wx. It was

Normal
chromosome 9

Abnormal
chromosome 9

Knob

Translocated
piece from
chromosome 8

(a) Normal and abnormal chromosome 9
c

Wx
Parental
chromosomes

C

wx
Crossing over

c

wx
Nonparental
chromosomes

C

Wx

(b) Crossing over between normal and abnormal
chromosome 9

F I G U R E 6 . 6 Crossing over between a normal and abnormal
chromosome 9 in corn. (a) A normal chromosome 9 in corn is compared to an abnormal chromosome 9 that contains a knob at one end
and a translocation at the opposite end. (b) A crossover produces a
chromosome that contains only a knob at one end and another chromosome that contains only a translocation at the other end.

crossed to a strain called parent B that carried two cytologically
normal chromosomes and had the genotype cc Wx wx.
They then observed the kernels in two ways. First, they
examined the phenotypes of the kernels to see if they were colored or colorless, and starchy or waxy. Second, the chromosomes
in each kernel were examined under a microscope to determine
their cytological appearance. Altogether, they observed a total of
25 kernels (see data of Figure 6.7).

THE HYPOTHESIS
Offspring with nonparental phenotypes are the product of a
crossover. This crossover should produce nonparental chromosomes via an exchange of chromosomal segments between
homologous chromosomes.

STEP 2: HYPOTHESIS
~bro25286_c06_126_159.indd 133

The student is given a statement describing
the possible explanation for the observed
phenomenon that will be tested. The
hypothesis section reinforces the scientific
method and allows students to experience
the process for themselves.

10/26/10 3:21 PM

xv

bro25286_FM.indd xv

12/6/10 12:57 PM


T E S T I N G T H E H Y P O T H E S I S — F I G U R E 6 . 7 Experimental correlation between genetic recombination and
crossing over.

Starting materials: Two different strains of corn. One strain, referred to as parent A, had an abnormal chromosome 9 (knobbed/translocation) with a dominant C allele and a recessive wx allele. It also had a cytologically normal copy of chromosome 9 that carried the recessive c allele and the dominant Wx allele. Its genotype was Cc Wxwx. The other strain (referred to as parent B) had two normal versions
of chromosome 9. The genotype of this strain was cc Wxwx.

1. Cross the two strains described. The
tassel is the pollen-bearing structure, and
the silk (equivalent to the stigma and
style) is connected to the ovary. After
fertilization, the ovary will develop into
an ear of corn.

STEP 3: TESTING THE
HYPOTHESIS

Conceptual level

Experimental level
Tassel
C

c

c

x

This section illustrates the
experimental process, including the
actual steps followed by scientists to
test their hypothesis. Science comes
alive for students with this detailed
look at experimentation.

c

x

Silk
wx

Parent A
Cc Wxwx

Wx

Wx

wx

Parent B
cc Wxwx

2. Observe the kernels from this cross.

F1 ear of corn

Each kernel is a separate seed that has
inherited a set of chromosomes from
each parent.

F1 kernels

STEP 4: THE DATA

T H E D ATA

Actual data from the original research
paper help students understand how
real-life research results are reported.
Each experiment’s results are
discussed in the context of the larger
genetic principle to help students
understand the implications and
importance of the research.

Phenotype of
F1 Kernel
Colored/waxy

Number of
Kernels
Analyzed

Cytological Appearance of Chromosome 9 in F1 Offspring*
Knobbed/translocation
Normal

3

Colorless/starchy

C
wx
Knobless/normal

11

c

Colorless/starchy

4

Knobless/translocation

Colorless/waxy

2

Knobless/translocation

Colored/starchy

5

Knobbed/normal

c

c
~bro25286_c06_126_159.indd 134

Wx

wx

wx

c
Normal
c

C
Total

STEP 5: INTERPRETING
THE DATA
This discussion, which examines whether
the experimental data supported or
refuted the hypothesis, gives students an
appreciation for scientific interpretation.

No

wx
No
or

Wx

c
Normal

wx

c

Wx

Yes

Normal

Yes

c
Normal

wx
Yes

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c

Did a Crossover
Occur During
Gamete Formation
in Parent A?

or

Wx

Wx

25

c

wx

*In this table, the chromosome on the left was inherited from parent A, and the blue chromosome on the right was inherited from parent B.
Data from Harriet B. Creighton and Barbara McClintock (1931) A Correlation of Cytological and Genetical Crossing-Over in Zea Mays. Proc. Natl. Acad. Sci.
USA 17, 492–497.

I N T E R P R E T I N G T H E D ATA
By combining the gametes in a Punnett square, the following
types of offspring can be produced:
Parent B
c Wx

c wx

Cc Wxwx

Cc wxwx

Colored,
starchy

Colored,
waxy

Nonrecombinant

C wx

cc WxWx

cc Wxwx

Colorless,
starchy

Colorless,
starchy

Nonrecombinant

arent A

c Wx

Parent A
C wx (nonrecombinant)
c Wx (nonrecombinant)
C Wx (recombinant)
c wx (recombinant)

Parent B
c Wx
c wx

As seen in the Punnett square, two of the phenotypic categories, colored, starchy (Cc Wx wx or Cc Wx Wx) and colorless,
starchy (cc Wx Wx or cc Wx wx), were ambiguous because they
could arise from a nonrecombinant and from a recombinant
gamete. In other words, these phenotypes could be produced
whether or not recombination occurred in parent A. Therefore,
let’s focus on the two unambiguous phenotypic categories: colored, waxy (Cc  wxwx) and colorless, waxy (cc wxwx). The colored, waxy phenotype could happen only if recombination did
not occur in parent A and if parent A passed the knobbed/

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End of Chapter Support Materials
These study tools and problems are crafted to aid students in reviewing key information in the text and developing a wide range
of skills. They also develop a student’s cognitive, writing, analytical, computational, and collaborative abilities.

KEY TERMS
Enhance student
development of vital
vocabulary necessary for
the understanding and
application of chapter
content. Important terms are
boldfaced throughout the
chapter and page referenced
at the end of each chapter
for reflective study.

CHAPTER SUMMARY
Emphasizes the main concepts from
each section of the chapter in a
bulleted form to provide students
with a thorough review of the main
topics covered.

CONCEPTUAL
QUESTIONS
Test the understanding of basic genetic
principles. The student is given many
questions with a wide range of difficulty.
Some require critical thinking skills, and
some require the student to write coherent
essay questions.

xvii

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EXPERIMENTAL
QUESTIONS
Test the ability to analyze data, design
experiments, or appreciate the relevance of
experimental techniques.

STUDENT DISCUSSION/
COLLABORATION
QUESTIONS
Encourage students to consider broad
concepts and practical problems. Some
questions require a substantial amount
of computational activities, which can be
worked on as a group.

xviii

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PA R T I

INTRODUCTION

C HA P T E R OU T L I N E
1.1

The Relationship Between Genes
and Traits

1.2

Fields of Genetics

1

Carbon copy, the first
cloned pet. In 2002, the
cat shown here, called
Carbon copy or Copycat,
was produced by cloning,
a procedure described in
Chapter 19.

OVERVIEW OF GENETICS

Hardly a week goes by without a major news story involving a
genetic breakthrough. The increasing pace of genetic discoveries has become staggering. The Human Genome Project is a case
in point. This project began in the United States in 1990, when
the National Institutes of Health and the Department of Energy
joined forces with international partners to decipher the massive amount of information contained in our genome—the DNA
found within all of our chromosomes (Figure 1.1). Working collectively, a large group of scientists from around the world has
produced a detailed series of maps that help geneticists navigate
through human DNA. Remarkably, in only a decade, they determined the DNA sequence (read in the bases of A, T, G, and C)
covering over 90% of the human genome. The first draft of this
sequence, published in 2001, is nearly 3 billion nucleotide base
pairs in length. The completed sequence, published in 2003, has
an accuracy greater than 99.99%; fewer than one mistake was
made in every 10,000 base pairs (bp)!
Studying the human genome allows us to explore fundamental details about ourselves at the molecular level. The results of the

Human Genome Project are expected to shed considerable light on
basic questions, like how many genes we have, how genes direct
the activities of living cells, how species evolve, how single cells

develop into complex tissues, and how defective genes cause disease. Furthermore, such understanding may lend itself to improvements in modern medicine by leading to better diagnoses of diseases and the development of new treatments for them.
As scientists have attempted to unravel the mysteries within
our genes, this journey has involved the invention of many new
technologies. For example, new technologies have made it possible
to produce medicines that would otherwise be difficult or impossible to make. An example is human recombinant insulin, sold
under the brand name Humulin. This medicine is synthesized in
strains of Escherichia coli bacteria that have been genetically altered
by the addition of genes that encode the polypeptides that form
human insulin. The bacteria are grown in a laboratory and make
large amounts of human insulin. As discussed in Chapter 19, the
insulin is purified and administered to many people with insulindependent diabetes.

1

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2

C H A P T E R 1 : : OVERVIEW OF GENETICS

Chromosomes

DNA, the molecule of life

Cell

Trillions of cells

Each cell contains:
• 46 human chromosomes,
found in 23 pairs
Gene
• 2 meters of DNA

G

T A

T A

C G

A T

A T

• Approximately 20,000 to
25,000 genes coding for
proteins that perform
most life functions

T A

T A

T A

C G

C G

• Approximately 3 billion
DNA base pairs per set
of chromosomes,
containing the bases A,
T, G, and C

DNA
mRNA

Amino acid

(a) The genetic composition of humans

Protein (composed of amino acids)

Chromosome 4
16
p 1

15

Huntington disease
Wolf-Hirschhorn syndrome
PKU due to dihydropteridine
reductase deficiency

13

1
13

Dentinogenesis imperfecta-1

24
26

q

28
31
3

32

35

Periodontitis, juvenile
Dysalbuminemic hyperzincemia
Dysalbuminemic hyperthyroxinemia
Analbuminemia
Hereditary persistence of alpha-fetoprotein
AFP deficiency, congenital
Piebaldism
Polycystic kidney disease, adult, type II
Mucolipidosis II
Mucolipidosis III

21

2

MPS 1 (Hurler and Scheie syndromes)
Mucopolysaccharidosis I

C3b inactivator deficiency
Aspartylglucosaminuria
Williams-Beuren syndrome, type II
Sclerotylosis
Anterior segment
mesenchymal dysgenesis
Pseudohypoaldosteronism
Hepatocellular carcinoma
Glutaric acidemia type IIC
Factor XI deficiency
Fletcher factor deficiency

Severe combined immunodeficiency due
to IL2 deficiency
Rieger syndrome

Dysfibrinogenemia, gamma types
Hypofibrinogenemia, gamma types
Dysfibrinogenemia, alpha types
Amyloidosis, hereditary renal
Dysfibrinogenemia, beta types
Facioscapulohumeral muscular dystrophy

(b) Genes on one human chromosome that are associated with disease when mutant

F I G U R E 1 . 1 The Human Genome Project. (a) The human genome is a complete set of human chromosomes. People have two sets of chromosomes, one from each parent. Collectively, each set of chromosomes is composed of a DNA sequence that is approximately 3 billion nucleotide base
pairs long. Estimates suggest that each set contains about 20,000 to 25,000 different genes. Most genes encode proteins. This figure emphasizes the
DNA found in the cell nucleus. Humans also have a small amount of DNA in their mitochondria, which has also been sequenced. (b) An important
outcome of genetic research is the identification of genes that contribute to human diseases. This illustration depicts a map of a few genes that are
located on human chromosome 4. When these genes carry certain rare mutations, they can cause the diseases designated in this figure.

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3

OVERVIEW OF GENETICS

New genetic technologies are often met with skepticism and
sometimes even with disdain. An example would be DNA fingerprinting, a molecular method to identify an individual based on
a DNA sample (see Chapter 24). Though this technology is now
relatively common in the area of forensic science, it was not always
universally accepted. High-profile crime cases in the news cause
us to realize that not everyone believes in DNA fingerprinting, in
spite of its extraordinary ability to uniquely identify individuals. A
second controversial example is mammalian cloning. In 1997, Ian
Wilmut and his colleagues created clones of sheep, using mammary cells from an adult animal (Figure 1.2). More recently, such
cloning has been achieved in several mammalian species, including
cows, mice, goats, pigs, and cats. In 2002, the first pet was cloned,
a cat named Carbon copy, or Copycat (see photo at the beginning
of the chapter). The cloning of mammals provides the potential

for many practical applications. With regard to livestock, cloning
would enable farmers to use cells from their best individuals to create genetically homogeneous herds. This could be advantageous
in terms of agricultural yield, although such a genetically homogeneous herd may be more susceptible to certain diseases. However, people have become greatly concerned with the possibility of
human cloning. This prospect has raised serious ethical questions.

Within the past few years, legislative bills have been introduced
that involve bans on human cloning.
Finally, genetic technologies provide the means to modify the
traits of animals and plants in ways that would have been unimaginable just a few decades ago. Figure 1.3a illustrates a bizarre example in which scientists introduced a gene from jellyfish into mice.
Certain species of jellyfish emit a “green glow” produced by a gene
that encodes a bioluminescent protein called green fluorescent protein (GFP). When exposed to blue or ultraviolet (UV) light, the
protein emits a striking green-colored light. Scientists were able to
clone the GFP gene from a sample of jellyfish cells and then introduce this gene into laboratory mice. The green fluorescent protein
is made throughout the cells of their bodies. As a result, their skin,
eyes, and organs give off an eerie green glow when exposed to UV
light. Only their fur does not glow.
The expression of green fluorescent protein allows researchers to identify particular proteins in cells or specific body parts. For

(a) GFP expressed in mice

GFP

(b) GFP expressed in the gonads of a male mosquito

F I G U R E 1 . 3 The introduction of a jellyfish gene into labora-

F I G U R E 1 . 2 The cloning of a mammal. The lamb on the left is
Dolly, the first mammal to be cloned. She was cloned from the cells of
a Finn Dorset (a white-faced sheep). The sheep on the right is Dolly’s
surrogate mother, a Blackface ewe. A description of how Dolly was produced is presented in Chapter 19.

bro25286_c01_001_016.indd 3

tory mice and mosquitoes. (a) A gene that naturally occurs in the
jellyfish encodes a protein called green fluorescent protein (GFP). The
GFP gene was cloned and introduced into mice. When these mice
are exposed to UV light, GFP emits a bright green color. These mice
glow green, just like jellyfish! (b) GFP was introduced next to a gene
sequence that causes the expression of GFP only in the gonads of male
mosquitoes. This allows researchers to identify and sort males from
females.

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4

C H A P T E R 1 :: OVERVIEW OF GENETICS

example, Andrea Crisanti and colleagues have altered mosquitoes
to express GFP only in the gonads of males (Figure 1.3b). This
enables the researchers to identify and sort males from females.
Why is this useful? The ability to rapidly sort mosquitoes makes
it possible to produce populations of sterile males and then release
the sterile males without the risk of releasing additional females.
The release of sterile males may be an effective means of controlling mosquito populations because females only breed once before
they die. Mating with a sterile male prevents a female from producing offspring. In 2008, Osamu Shimomura, Martin Chalfie,
and Roger Tsien received the Nobel Prize in chemistry for the discovery and the development of GFP, which has become a widely
used tool in biology.
Overall, as we move forward in the twenty-first century, the

excitement level in the field of genetics is high, perhaps higher
than it has ever been. Nevertheless, the excitement generated by
new genetic knowledge and technologies will also create many
ethical and societal challenges. In this chapter, we begin with an
overview of genetics and then explore the various fields of genetics
and their experimental approaches.

1.1 THE RELATIONSHIP BETWEEN

GENES AND TRAITS

Genetics is the branch of biology that deals with heredity and
variation. It stands as the unifying discipline in biology by allowing us to understand how life can exist at all levels of complexity, ranging from the molecular to the population level. Genetic
variation is the root of the natural diversity that we observe
among members of the same species as well as among different
species.
Genetics is centered on the study of genes. A gene is classically defined as a unit of heredity, but such a vague definition
does not do justice to the exciting characteristics of genes as
intricate molecular units that manifest themselves as critical contributors to cell structure and function. At the molecular level, a
gene is a segment of DNA that produces a functional product.
The functional product of most genes is a polypeptide, which is
a linear sequence of amino acids that folds into units that constitute proteins. In addition, genes are commonly described
according to the way they affect traits, which are the characteristics of an organism. In humans, for example, we speak of traits
such as eye color, hair texture, and height. The ongoing theme of
this textbook is the relationship between genes and traits. As an
organism grows and develops, its collection of genes provides a
blueprint that determines its characteristics.
In this section of Chapter 1, we examine the general features
of life, beginning with the molecular level and ending with populations of organisms. As will become apparent, genetics is the common
thread that explains the existence of life and its continuity from generation to generation. For most students, this chapter should serve

as a cohesive review of topics they learned in other introductory
courses such as General Biology. Even so, it is usually helpful to see
the “big picture” of genetics before delving into the finer details that
are covered in Chapters 2 through 26.

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Living Cells Are Composed of Biochemicals
To fully understand the relationship between genes and traits, we
need to begin with an examination of the composition of living
organisms. Every cell is constructed from intricately organized
chemical substances. Small organic molecules such as glucose and
amino acids are produced from the linkage of atoms via chemical
bonds. The chemical properties of organic molecules are essential
for cell vitality in two key ways. First, the breaking of chemical
bonds during the degradation of small molecules provides energy
to drive cellular processes. A second important function of these
small organic molecules is their role as the building blocks for the
synthesis of larger molecules. Four important categories of larger
cellular molecules are nucleic acids (i.e., DNA and RNA), proteins, carbohydrates, and lipids. Three of these—nucleic acids,
proteins, and carbohydrates—form macromolecules that are composed of many repeating units of smaller building blocks. Proteins,
RNA, and carbohydrates can be made from hundreds or even
thousands of repeating building blocks. DNA is the largest macromolecule found in living cells. A single DNA molecule can be composed of a linear sequence of hundreds of millions of nucleotides!
The formation of cellular structures relies on the interactions of molecules and macromolecules. For example, nucleotides are the building blocks of DNA, which is a constituent
of cellular chromosomes (Figure 1.4). In addition, the DNA is
associated with a myriad of proteins that provide organization
to the structure of chromosomes. Within a eukaryotic cell, the
chromosomes are contained in a compartment called the cell
nucleus. The nucleus is bounded by a double membrane composed of lipids and proteins that shields the chromosomes from
the rest of the cell. The organization of chromosomes within a

cell nucleus protects the chromosomes from mechanical damage
and provides a single compartment for genetic activities such as
gene transcription. As a general theme, the formation of large
cellular structures arises from interactions among different molecules and macromolecules. These cellular structures, in turn, are
organized to make a complete living cell.

Each Cell Contains Many Different Proteins That
Determine Cellular Structure and Function
To a great extent, the characteristics of a cell depend on the types
of proteins that it makes. All of the proteins that a cell makes at
a given time is called its proteome. As we will learn throughout this textbook, proteins are the “workhorses” of all living cells.
The range of functions among different types of proteins is truly
remarkable. Some proteins help determine the shape and structure of a given cell. For example, the protein known as tubulin
can assemble into large structures known as microtubules, which
provide the cell with internal structure and organization. Other
proteins are inserted into cell membranes and aid in the transport of ions and small molecules across the membrane. Proteins
may also function as biological motors. An interesting case is
the protein known as myosin, which is involved in the contractile properties of muscle cells. Within multicellular organisms,
certain proteins also function in cell-to-cell recognition and signaling. For example, hormones such as insulin are secreted by

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