Genetics for Dummies

Your no-nonsense guide to genetics

With rapid advances in genomic technologies, genetic testing has become a key part of both clinical practice and research. Scientists are constantly discovering more about how genetics plays a role in health and disease, and healthcare providers are using this information to more accurately identify their patients' particular medical needs. Genetic information is also increasingly being used for a wide range of non-clinical purposes, such as exploring one's ancestry.

This new edition of Genetics For Dummies serves as a perfect course supplement for students pursuing degrees in the sciences. It also provides science-lovers of all skill levels with easy-to-follow and easy-to-understand information about this exciting and constantly evolving field. This edition includes recent developments and applications in the field of genetics, such as:

• Whole-genome and whole-exome sequencing
• Precision medicine and pharmacogenetics
• Direct-to-consumer genetic testing for health risks
• Ancestry testing

Featuring information on some of the hottest topics in genetics right now, this book makes it easier than ever to wrap your head around this fascinating subject.

Tara Rodden Robinson, PhD, was an instructor and Postdoctoral Fellow in Genetics in the Department of Biological Sciences at Auburn University. She has also been an instructor at Oregon State University. Lisa Cushman Spock, PhD, CGC, is a clinical genomics specialist and former genetics counselor at Indiana University School of Medicine.

Introduction 1

About This Book 1

Conventions Used in This Book 2

Foolish Assumptions 2

How This Book is Organized 3

Part 1: The Lowdown on Genetics: Just the Basics 3

Part 2: DNA: The Genetic Material 3

Part 3: Genetics and Your Health 3

Part 4: Genetics and Your World 3

Part 5: The Part of Tens 4

Icons Used in This Book 4

Beyond This Book 4

Where to Go from Here 5

Part 1: The Lowdown on Genetics: Just the Basics 7

Chapter 1: Welcome to Genetics: What’s What and Who’s Who 9

What is Genetics? 9

Classical genetics: Transmitting traits from generation to generation 10

Molecular genetics: DNA and the chemistry of genes 11

Population genetics: Genetics of groups 12

Quantitative genetics: Getting a handle on heredity 13

Genetics as a Career 13

Exploring a genetics lab 14

Sorting through jobs in genetics 15

Chapter 2: Basic Cell Biology 21

Looking Around Your Cell 22

Cells without a nucleus 22

Cells with a nucleus 23

What’s in a nucleus? 25

Examining the basics of chromosomes 25

So Where Are My Genes? 27

Mitosis: Splitting Up 29

Step 1: Time to grow 30

Step 2: Divvying up the chromosomes 31

Step 3: The big divide 33

Meiosis: Making Cells for Reproduction 34

Meiosis I 35

Meiosis II 37

Mommy, where did I come from? 38

Chapter 3: Visualize Peas: Discovering the Laws of Inheritance 41

Gardening with Gregor Mendel 42

Speaking the Language of Inheritance 44

Simplifying Inheritance 45

Establishing dominance 45

Segregating alleles 47

Declaring independence 48

Finding Unknown Alleles 50

Applying Basic Probability to the Likelihood of Inheritance 50

Solving Simple Genetics Problems 52

Deciphering a monohybrid cross 53

Tackling a dihybrid cross 53

Chapter 4: Law Enforcement: Mendel’s Laws Applied to Complex Traits 57

Dominant Alleles Rule Sometimes 58

Wimping out with incomplete dominance 58

Keeping it fair with codominance 59

Dawdling with incomplete penetrance 60

Alleles Causing Complications 61

More than two alleles 61

Lethal alleles 63

Making Life More Complicated 63

When genes interact 63

Genes in hiding 65

Genes linked together 66

One gene with many phenotypes 69

Uncovering More Exceptions to Mendel’s Laws 70

Epigenetics 70

Genomic imprinting 70

Anticipation 71

Environmental effects 72

Part 2: DNA: The Genetic Material 73

Chapter 5: DNA: The Basis of Life 75

Chemical Ingredients of DNA 76

Covering the bases 76

Adding a spoonful of sugar and a little phosphate 78

Assembling the Double Helix: The Structure of DNA 79

Starting with one: Weaving a single strand 79

Doubling up: Adding the second strand 81

Examining Different Varieties of DNA 85

Nuclear DNA 85

Mitochondrial DNA 85

Chloroplast DNA 86

Digging into the History of DNA 87

Discovering DNA 87

Obeying Chargaff’s rules 88

Hard feelings and the helix: Franklin, Wilkins, Watson, and Crick 88

Chapter 6: Chromosomes: The Big Picture 91

Deconstructing the Double Helix 92

Anatomy of a Chromosome 93

Two Chromosomes Are Better than One (or Three) 95

Sex Chromosomes: Is It a Boy or Girl? 96

Sex determination in humans 97

Sex determination in other organisms 101

Chapter 7: Replication: A Copy Machine for DNA 105

Unzipped: Creating the Pattern for More DNA 106

How DNA Copies Itself 109

Meeting the replication crew 110

Splitting the helix 113

Priming the pump 115

Leading and lagging 115

Joining all the pieces 117

Proofreading replication 117

Replication in Eukaryotes 118

Pulling up short: Telomeres 118

Finishing the job 120

How Circular DNAs Replicate 120

Theta 121

Rolling circle 121

D-loop 122

Chapter 8: DNA Sequencing: Decoding the Genome 123

Sequencing: Reading the Language of DNA 124

Identifying the players in DNA sequencing 124

Finding the message in sequencing results 127

Newer, cheaper, faster 127

Sequencing Your Way to the Human Genome 129

The Human Genome Project 130

Trying on a Few Genomes 132

The yeast genome 134

The elegant roundworm genome 134

The chicken genome 135

Chapter 9: RNA: DNA’s Close Cousin 137

You Already Know a Lot about RNA 137

Using a slightly different sugar 138

Meeting a new base: Uracil 139

Stranded! 140

Transcription: Copying DNA’s Message into RNA’s Language 141

Getting ready to transcribe 142

Initiation 146

Elongation 147

Termination 147

Post-transcription Processing 148

Adding cap and tail 148

Editing the message 149

Chapter 10: Translating the Genetic Code 151

Discovering the Good in a Degenerate 152

Considering the combinations 153

Framed! Reading the code 154

Not quite universal 155

Meeting the Translating Team 155

Taking the Translation Trip 156

Initiation 156

Elongation 159

Termination 160

Proteins Are Precious Polypeptides 162

Recognizing radical groups 162

Giving the protein its shape 162

Chapter 11: Gene Expression: What a Cute Pair of Genes 165

Getting Your Genes Under Control 166

To Be Expressed or Not To Be Expressed? 166

Regulating Gene Expression: A Time and Place for Everything 168

Controlling Transcription Before It Starts 169

Regulation of Gene Transcription: Flipping the Switch 170

Sequences controlling genes 170

Proteins controlling transcription 172

Hormones controlling transcription 173

Retroactive Control: Things That Happen after Transcription 174

Nip and tuck: RNA splicing 175

Shut up! mRNA silencing 175

mRNA expiration dates 177

Gene Control Lost in Translation 177

Modifying where translation occurs 177

Modifying when translation occurs 178

Modifying the protein shape 179

Prokaryotic Gene Expression 179

Bacterial gene organization 179

Bacterial gene expression 180

Part 3: Genetics and Your Health 181

Chapter 12: When Things Go Wrong: Changes in DNA Sequence 183

Heritable or Not Heritable? 184

Facing the Consequences of Sequence Variants 184

Sorting Out Terminology 185

The phenotypic effect of a DNA sequence change 185

The type of DNA sequence change 186

What Causes Sequence Variants? 189

Spontaneous sequence variants 190

Induced sequence variants 194

Evaluating Options for DNA Repair 198

Chapter 13: Chromosome Disorders: It’s All a Numbers Game 199

Chromosome Numbers: No More and No Less 200

Aneuploidy: Extra or missing chromosomes 200

Aneuploidy of the Autosomal Chromosomes 202

When chromosomes go missing 202

When too many chromosomes are left in 202

Aneuploidy of the Sex Chromosomes 205

Extra Xs 205

Extra Ys 206

Monosomy X 206

Exploring Variations in Chromosome Structure 206

Duplications 207

Deletions 208

Inversions 208

Translocations 209

Reciprocal translocations 209

Robertsonian translocations 210

Other things that go awry with chromosomes 211

How Chromosomes Are Studied 212

Big enough to see 212

Too small for the naked eye 214

Non-Invasive Prenatal Testing for Aneuploidy 215

Chapter 14: Taking a Closer Look at the Genetics of Cancer 217

Defining Cancer 218

Benign growths: Not always so harmless 218

Malignancies: Seriously scary results 219

Metastasis: Cancer on the move 220

Recognizing Cancer as a DNA Disease 221

Exploring the cell cycle and cancer 222

Demystifying chromosome abnormalities 228

Breaking Down the Types of Cancers 229

Hereditary Breast Cancer 231

Hereditary colorectal cancer 232

Chapter 15: Genetic Counseling, Risk Assessment, and Genetic Testing 235

Getting to Know Genetic Counselors 236

Building and Analyzing a Family Tree 237

Autosomal Inheritance: No Differences Among the Sexes 240

Autosomal dominant traits and disorders 240

Autosomal recessive traits and disorders 241

Found on Sex Chromosomes: Sex-linked Inheritance 244

X-linked recessive traits 245

X-linked dominant traits 247

Y-linked traits 248

Sex-limited traits 249

Sex-influenced traits 249

Testing for Genetic Disorders 249

Diagnostic testing 251

Prenatal diagnosis 251

Carrier testing 252

Predictive and susceptibility testing 252

Preimplantation genetic diagnosis 253

Pharmacogenetic testing 254

Chapter 16: Treating Genetic Disorders and Using Genetics to Tailor Treatment 255

Alleviating Genetic Disease through Gene Therapy 256

Inserting Healthy Genes into the Picture 256

Finding Vehicles to Get Genes to Work 259

Viruses that join right in 260

Viruses that are a little standoffish 261

Progress on the Gene Therapy Front 261

Utilizing Genetic Information for Precision Medicine 263

Pharmacogenetics (and pharmacogenomics) 263

Cytochrome P450 and drug metabolism 264

Decreasing the risk of side effects of treatment 266

Increasing the effectiveness of treatment 266

Part 4: Genetics and Your World 269

Chapter 17: Tracing Human History and the Future of the Planet 271

Genetic Variation is Everywhere 272

Allele frequencies 272

Genotype frequencies 274

Breaking Down the Hardy-Weinberg Law of Population Genetics 275

Relating alleles to genotypes 275

Violating the law 277

Mapping the Gene Pool 279

One big happy family 279

Ancestry testing 280

Uncovering the secret social lives of animals 281

Changing Forms over Time: The Genetics of Evolution 282

Genetic variation is key 283

Where new species come from 283

Growing the evolutionary tree 284

Chapter 18: Solving Mysteries Using DNA 287

Rooting through Your DNA to Find Your Identity 288

Investigating the Scene: Where’s the DNA? 290

Collecting biological evidence 290

Moving to the lab 292

Employing DNA to Catch Criminals (And Free the Innocent) 297

Matching the evidence to the bad guy 297

Taking a second look at guilty verdicts 299

It’s All Relative: Finding Family 300

Paternity testing 300

Relatedness testing 302

Chapter 19: Genetic Makeovers: Using Genetic Engineering to Change the Genome 307

Genetically Modified Organisms Are Everywhere 308

Old Genes in New Places 309

Following the transgenesis process 311

Making a transgene using recombinant DNA technology 311

Modifying the gene to reside in its new home 313

Looking at the GMO Menagerie 313

Transgenic animals 313

Transgenic insects 316

Transgenic bacteria 316

Transgenic plants 318

Getting new genes into the plant 318

Exploring commercial applications 319

Weighing points of contention 320

Changing the Blueprint: Gene Editing 321

CRISPR-Cas9 gene editing 323

Germline versus somatic gene editing 325

Discussing the ethics of gene editing 325

Chapter 20: Giving Ethical Considerations Their Due 327

Profiling Genetic Discrimination 327

Ordering Up Designer Babies 329

Ethical Issues Surrounding Genetic Testing 330

Informed Consent 331

Patient Autonomy 333

Privacy and Confidentiality 334

Incidental Findings 335

Direct-to-Consumer Testing 336

Practicing Safe Genetic Treatments 337

Genetic Property Rights 338

Part 5: The Part of Tens 339

Chapter 21: Ten Defining Events in Genetics 341

The Publication of Darwin’s “The Origin of Species” 341

The Rediscovery of Mendel’s Work 342

DNA Transformation 343

The Discovery of Jumping Genes 344

The Birth of DNA Sequencing 345

The Invention of PCR 345

The Development of Recombinant DNA Technology 346

The Invention of DNA Fingerprinting 347

The Birth of Developmental Genetics 347

The Work of Francis Collins and the Human Genome Project 348

Chapter 22: Ten Hot Issues in Genetics 349

Direct-to-Consumer Genetic Testing 349

Whole Exome Sequencing 350

Whole Genome Sequencing 352

Stem Cell Research 352

The ENCODE Project 353

Proteomics 354

Gene Chips 355

Evolution of Antibiotic Resistance 356

Circumventing Mother Nature 356

Genetics from Afar 357

Glossary 359

Index 365

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