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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
- Veröffentlichungsjahr: 2023
Evolve your knowledge of the fast-moving world of genetic research Genetics For Dummies shines a light on the fascinating field of genetics, helping you gain a greater understanding of how genetics factors into everyday life. Perfect as a supplement to a genetics course or as an intro for the curious, this book is packed with easy-to-understand explanations of the key concepts, including an overview of cell biology. You'll also find tons of coverage of recent discoveries in the field, plus info on how genetics can affect your health and wellbeing. Whole-genome sequencing, genetic disease treatments, exploring your ancestry, non-invasive prenatal testing--it's all here, in the friendly and relatable Dummies style you love. * Grasp the basics of cell biology and get a primer on the field of genetic research * Discover what you can learn about yourself, thanks to advances in genetic testing * Learn how your genes influence your health and wellbeing, today and as you age * Follow along with your college-level genetics course--or refresh your knowledge--with clear explanations of complex ideas Genetics For Dummies is great for students of the biological sciences, and for the genetically curious everywhere.
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Table of Contents
Cover
Title Page
Copyright
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond This Book
Where to Go from Here
Part 1: The Lowdown on Genetics: Just the Basics
Chapter 1: Welcome to Genetics: Just About Everyone Loves a Good Pair of Genes
Unwrapping Life’s Secrets
Classical Genetics: Studying How Traits Are Transmitted within Families
Molecular Genetics: Diving into DNA Science
Population Genetics: Studying the Genetics of Groups
Quantitative Genetics: Exploring the Heredity of Complex Traits
Chapter 2: Basic Cell Biology
Entering the World of the Cell
Exploring Your DNA, Chromosomes, and Genes
Mitosis: Splitting Up
Meiosis: Making Cells for Sexual Reproduction
Chapter 3: Visualize Peas: Discovering the Laws of Inheritance
Gardening with Gregor Mendel
Speaking the Language of Inheritance
Simplifying Inheritance
Finding Unknown Alleles
Applying Basic Probability to the Likelihood of Inheritance
Solving Genetics Problems
Chapter 4: Law Enforcement: Mendel’s Laws Applied to Complex Traits
Dominant Alleles Rule … Sometimes
Alleles Causing Complications
Making Life More Complicated
Uncovering More Exceptions to Mendel’s Laws
Part 2: DNA: The Genetic Material
Chapter 5: DNA: The Pattern for Life
Chemical Ingredients of DNA
Assembling the Double Helix: The Structure of DNA
Examining Different Varieties of DNA
Digging into the History of DNA
Chapter 6: Chromosomes: The Big Picture
Packaging the Double Helix
Anatomy of a Chromosome
Two Chromosomes Are Better than One (or Three)
Sex Chromosomes: Is It a Boy or Girl?
Chapter 7: Replication: A Copy Machine for DNA
Unzipped: Creating the Pattern for More DNA
How DNA Copies Itself
Replication in Eukaryotes
How Circular DNAs Replicate
Chapter 8: Transcription: Getting Instructions from DNA
RNA: DNA’s Close Cousin
Transcription: Copying DNA’s Message into RNA’s Language
Post-transcription Processing
Chapter 9: Translating the Genetic Code
Discovering the Good in a Degenerate
Meeting the Translating Team
Taking the Translation Trip
Proteins Are Powerful
Chapter 10: Gene Expression: Finding the Right Tool for the Job
Getting Your Genes Under Control
To Be Expressed or Not To Be Expressed?
Regulating Eukaryotic Gene Expression: A Time and Place for Everything
Controlling Transcription Before It Starts
Regulation of Gene Transcription: Flipping the Switch
Post-transcriptional Control
Gene Control Lost in Translation
Prokaryotic Gene Expression
Part 3: Genetics and Your Health
Chapter 11: What Could Go Wrong: Changes in DNA Sequence
Heritable or Not Heritable?
Facing the Consequences of Sequence Variants
Sorting Out Terminology
What Causes Sequence Variants?
Evaluating Options for DNA Repair
Chapter 12: Chromosome Disorders: It’s All a Numbers Game
Chromosome Numbers: No More and No Less
Aneuploidy of the Autosomal Chromosomes
Aneuploidy of the Sex Chromosomes
Exploring Variations in Chromosome Structure
How Chromosomes Are Studied
Non-Invasive Prenatal Testing for Aneuploidy
Chapter 13: Taking a Closer Look at the Genetics of Cancer
Defining Cancer
Recognizing Cancer as a DNA Disease
Breaking Down the Types of Cancers
Chapter 14: Genetic Counseling, Risk Assessment, and Genetic Testing
Getting to Know Genetic Counselors
Building and Analyzing a Family Tree
Autosomal Inheritance: No Differences Among the Sexes
Found on Sex Chromosomes: Sex-linked Inheritance
Testing for Genetic Disorders
Chapter 15: Treating Genetic Disorders and Using Genetics to Tailor Treatment
Alleviating Genetic Disease through Gene Therapy
Inserting Healthy Genes into the Picture
Finding Vehicles to Get Genes to Work
Progress on the Gene Therapy Front
Utilizing Genetic Information for Precision Medicine
Part 4: Genetics and Your World
Chapter 16: Tracing Human History and the Future of Populations
Genetic Variation Is Everywhere
Breaking Down the Hardy-Weinberg Law of Population Genetics
Mapping the Gene Pool
Changing Forms over Time: The Genetics of Evolution
Chapter 17: Solving Mysteries Using DNA
Rooting through Your DNA to Find Your Identity
Investigating the Scene: Where’s the DNA?
Employing DNA to Catch Criminals (And Free the Innocent)
It’s All Relative: Finding Family
Chapter 18: DNA Sequencing: Decoding the Genome
Sequencing: Reading the Language of DNA
Sequencing Your Way to the Human Genome
Trying on a Few Genomes
Chapter 19: Genetic Makeovers: Using Genetic Engineering to Change the Genome
Genetically Modified Organisms Are Everywhere
Old Genes in New Places
Looking at the GMO Menagerie
Transgenic Plants
Changing the Blueprint: Gene Editing
Chapter 20: Giving Ethical Considerations Their Due
Profiling Genetic Discrimination
Ordering Up Designer Babies
Ethical Issues Surrounding Genetic Testing
Practicing Safe Genetic Treatments
Genetic Property Rights
Part 5: The Part of Tens
Chapter 21: Ten Hot Issues in Genetics
Direct-to-Consumer Genetic Testing
Whole Exome Sequencing
Whole Genome Sequencing
Stem Cell Research
The ENCODE Project
Proteomics
Gene Chips
Evolution of Antibiotic Resistance
Circumventing Mother Nature
Genetics from Afar
Chapter 22: Ten Pathways to a Career in Genetics
Laboratory Technicians
Graduate Student
Post-doctoral Fellows
Research Scientist
College or University Professor
Clinical Laboratory Director
Clinical Geneticist
Genetic Counselor
Genetic Counseling Assistant
Forensic Geneticist
Index
About the Authors
Advertisement Page
Connect with Dummies
End User License Agreement
List of Tables
Chapter 3
TABLE 3-1 Seven Traits of Pea Plants Studied by Gregor Mendel
Chapter 4
TABLE 4-1 Genetics of Hair Color in Horses
TABLE 4-2 Linked Traits in a Dihybrid Test Cross
Chapter 11
TABLE 11-1 Types and Effects of DNA Sequence Variants
Chapter 13
TABLE 13-1 Lifetime Probability of Developing Cancer
TABLE 13-2 Types of Cancer
Chapter 15
TABLE 15-1 Common Viral Vectors for Gene Therapy
TABLE 15-2 Metabolism of Medications by the CYP2D6 Enzyme
Chapter 18
TABLE 18-1 Major Milestones in DNA Sequencing
TABLE 18-2 Genome Sizes of Various Organisms
List of Illustrations
Chapter 2
FIGURE 2-1: A prokaryotic cell (a) is very simple compared to a eukaryotic cell...
FIGURE 2-2: The Human Life Cycle.
FIGURE 2-3: The 46 human chromosomes are divided into 23 pairs.
FIGURE 2-4: Basic structure of eukaryotic chromosomes.
FIGURE 2-5: The cell cycle: mitosis, cell division, and all points in between.
FIGURE 2-6: The process of mitosis, broken into four stages: prophase, metaphas...
FIGURE 2-7: The phases of meiosis.
FIGURE 2-8: Crossing-over creates unique combinations of alleles during meiosis...
FIGURE 2-9: Gametogenesis in humans.
Chapter 3
FIGURE 3-1: Reproductive parts of a flower.
FIGURE 3-2: Alleles are arranged in loci on chromosomes.
FIGURE 3-3: Monohybrid crosses illustrate how simple inheritance works.
FIGURE 3-4: The principles of segregation and dominance as illustrated by three...
FIGURE 3-5: The results of test crosses reveal unknown genotypes.
FIGURE 3-6: Genotypes and phenotypes resulting from a dihybrid cross.
FIGURE 3-7: A Punnett square of a dihybrid cross.
Chapter 4
FIGURE 4-1: Human blood type.
FIGURE 4-2: Genes interact to produce pigment in this dihybrid cross for pepper...
FIGURE 4-3: Linked genes occur on the same chromosome and are inherited togethe...
FIGURE 4-4: Typical results of a dihybrid test cross when traits assort indepen...
FIGURE 4-5: A dihybrid cross with linked genes.
Chapter 5
FIGURE 5-1: The four DNA bases.
FIGURE 5-2: The chemical structure of ribose and deoxyribose.
FIGURE 5-3: Chemical structures of the four nucleotides present in DNA.
FIGURE 5-4: The chemical structures of DNA.
FIGURE 5-5: Antiparallel strands of DNA.
FIGURE 5-6: The DNA double helix.
Chapter 6
FIGURE 6-1: DNA is wrapped around nucleosomes and tightly coiled to fit into ti...
FIGURE 6-2: Chromosome features are evident in a metaphase chromosome.
FIGURE 6-3: Classification of chromosomes based on centromere location.
FIGURE 6-4: A human karyotype showing twenty-two pairs of autosomes and two sex...
FIGURE 6-5: Human X and Y chromosomes.
Chapter 7
FIGURE 7-1: DNA provides its own pattern for copying itself using semiconservat...
FIGURE 7-2: Conservative replication.
FIGURE 7-3: The results of Taylor, Woods, and Hughes experiment show that DNA r...
FIGURE 7-4: Connecting the chemical building blocks (nucleotides as dNTPs) duri...
FIGURE 7-5: The process of replication.
FIGURE 7-6: Leading and lagging strands.
FIGURE 7-7: Telomeres require special help to replicate during meiosis.
FIGURE 7-8: Circular DNA can be replicated in one of three ways.
Chapter 8
FIGURE 8-1: The ribose sugar is part of RNA.
FIGURE 8-2: The four bases found in RNA.
FIGURE 8-3: Single-stranded RNAs form interesting shapes in order to carry out ...
FIGURE 8-4: Transcription results in an RNA transcript, while translation resul...
FIGURE 8-5: The transcription unit is made up of a promoter, the gene, and a te...
FIGURE 8-6: The basic building blocks of RNA and the chemical structure of an R...
FIGURE 8-7: Transcribing DNA’s message into RNA.
FIGURE 8-8: A 5′ cap, 3′ poly-A tail, and alternative splicing.
Chapter 9
FIGURE 9-1: The 64 codons of the genetic code, as written by mRNA.
FIGURE 9-2: The genetic code is nonoverlapping and uses a reading frame.
FIGURE 9-3: tRNA has a unique shape that helps it ferry amino acids to the ribo...
FIGURE 9-4: tRNA charging.
FIGURE 9-5: Initiation and elongation during translation.
FIGURE 9-6: Termination of translation.
FIGURE 9-7: The 20 amino acids used to construct proteins.
FIGURE 9-8: Proteins are folded into complex, three-dimensional shapes.
FIGURE 9-9: Interactions between R groups form the bonds that stabilize protein...
Chapter 10
FIGURE 10-1: The genes that produce different kinds of hemoglobin get turned on...
FIGURE 10-2: Gene regulation in eukaryotes.
FIGURE 10-3: Transcription factors in eukaryotic cells.
FIGURE 10-4: mRNAs have untranslated regions (UTRs) at the 5′ and 3′ ends.
FIGURE 10-5: Organization of bacterial genes in an operon.
Chapter 11
FIGURE 11-1: Wobble pairing allows mismatched bases to form bonds.
FIGURE 11-2: A mismatched base pair creates a permanent change in the DNA with ...
FIGURE 11-3: Strand slippage causes loops to form during replication, resulting...
FIGURE 11-4: Deamination converts cytosine to uracil.
FIGURE 11-5: Base analogs, such as 5-bromouracil, are very similar to normal ba...
FIGURE 11-6: Intercalating agents fit between the stacks of bases to disfigure ...
FIGURE 11-7: Adjacent thymines can bond together to form dimers, which damage t...
FIGURE 11-8: DNA repair mechanisms.
Chapter 12
FIGURE 12-1: The results of nondisjunction during meiosis.
FIGURE 12-2: Risk of having a child with Down syndrome increases with maternal ...
FIGURE 12-3: Common types of chromosomal rearrangements.
FIGURE 12-4: Unequal crossover events cause large-scale deletions of chromosome...
FIGURE 12-5: A translocation that leads to familial Down syndrome.
FIGURE 12-6: Banding pattern of chromosome 22.
FIGURE 12-7: Microarray analysis used to test for chromosome imbalances.
Chapter 13
FIGURE 13-1: Normal cells and malignant cells look very different.
FIGURE 13-2: Tumors start out from mutations in the DNA of one cell.
FIGURE 13-3: Quality control points in the cell cycle protect your cells from m...
FIGURE 13-4: The Two-Hit Hypothesis.
FIGURE 13-5: The Philadelphia chromosome.
Chapter 14
FIGURE 14-1: Symbols commonly used in the pedigree analysis.
FIGURE 14-2: A typical family tree with an autosomal dominant inheritance patte...
FIGURE 14-3: An example of an autosomal recessive disorder in a family tree.
FIGURE 14-4: The X-linked recessive disorder hemophilia works its way through t...
FIGURE 14-5: A family tree showing inheritance of an X-linked dominant trait.
FIGURE 14-6: Pedigree for a Y-linked trait.
Chapter 15
FIGURE 15-1: Gene therapy in humans.
Chapter 16
FIGURE 16-1: Allele and genotype frequencies. (
Note:
Each circle represents ten...
FIGURE 16-2: The Hardy-Weinberg graph describes the relationship between allele...
FIGURE 16-3: Natural selection.
FIGURE 16-4: An evolutionary tree can show common ancestry among species.
Chapter 17
FIGURE 17-1: Alleles of two STR loci on the chromosomes of two suspects (S1 and...
FIGURE 17-2: The process of PCR.
FIGURE 17-3: The number of STR copies made by five cycles of PCR.
FIGURE 17-4: The process of gel electrophoresis.
FIGURE 17-5: The DNA fingerprints of two suspects (S1 and S2) are compared with...
FIGURE 17-6: Paternity testing using STR loci.
Chapter 18
FIGURE 18-1: Comparison of the chemical structure of a generic dNTP (left) and ...
FIGURE 18-2: DNA sequencing.
FIGURE 18-3: Results of a typical sequencing reaction.
Chapter 19
FIGURE 19-1: Restriction enzymes.
FIGURE 19-2: Cloning a gene.
FIGURE 19-3: Researchers introduce transgenes into mouse embryos before fertili...
FIGURE 19-4: The use of transgenic bacteria to make human insulin.
FIGURE 19-5:
Agrobacterium
inserts its genes into plant cells to cause gall for...
FIGURE 19-6: The CRISPR-Cas9 system in bacteria.
FIGURE 19-7: Gene editing using the CRISPR-Cas9 system.
Guide
Cover
Table of Contents
Title Page
Copyright
Begin Reading
Index
About the Authors
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Genetics For Dummies®,4th Edition
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
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Introduction
Genetics seeks to understand how the traits of all living things are determined. Although sometimes complicated and always diverse, all genetics comes down to basic principles of heredity — how traits are passed from one generation to the next — and how DNA is put together. As a science, genetics is a fast-growing field because of its untapped potential — for good and for bad. Despite its complexity, genetics can be surprisingly accessible. Genetics is a bit like peeking behind a movie’s special effects to find a deceptively simple and elegant system running the whole show.
About This Book
Genetics For Dummies, 4th Edition, is an overview of the entire field of genetics. Our goal is to explain every topic so that anyone, even someone without any genetics background at all, can follow the subject and understand how it works. As in the first three editions, we include many examples from the frontiers of research. We also make sure that the book has detailed coverage of some of the hottest topics that you hear about in the news, including gene therapy, pharmacogenetics, and gene editing. And we address the practical side of genetics: how it affects your health and the world around you. In short, this book is designed to be a solid introduction to genetics basics and to provide some details on the subject.
Genetics is a fast-paced field; new discoveries are coming out all the time. You can use this book to help you get through your genetics course or for self-guided study. Genetics For Dummies, 4th Edition, provides enough information for you to get a handle on the latest press coverage, understand the genetics jargon that mystery writers like to toss around, and translate information imparted to you by medical professionals. The book is filled with stories of key discoveries and “wow” developments. Although we try to keep things light and inject some humor when possible, we also make every effort to be sensitive to whatever your circumstances may be.
This book is a great guide if you know nothing at all about genetics. If you already have some background, then you’re set to dive into the details of the subject and expand your horizons.
It would be very easy for us to use specialized language that you’d need a translator to understand, but what fun would that be? Throughout this book, we try to avoid jargon as much as possible, but at the same time, we use and carefully define terms that scientists actually use. After all, it may be important for you to understand some of these terms in the course of your studies or your or a loved one’s medical treatment.
To help you navigate through this book, we use the following typographical conventions:
We use
italic
for emphasis and to highlight new words or terms that we define in the text. The names of genes are also italicized because that is standard practice in the field of genetics.
We use
boldface
to indicate keywords in bulleted lists or the action parts of numbered steps.
We use
monofont
for websites and email addresses.
We designed this book to cover background material in the first two parts and then all the applications in the rest of the book. We think you’ll find it quite accessible.
Part 1, “The Lowdown on Genetics: Just the Basics”:
Part 1
explains how traits are inherited. The first chapter introduces you to the field of genetics. The second chapter gives you a handle on how genetic information gets divided up during cell division; these events provide the foundation for just about everything else that has to do with genetics. From there, we explain simple inheritance of one gene and then move on to more complex forms of inheritance.
Part 2, “DNA: The Genetic Material”:
Part 2
covers what’s sometimes called
molecular genetics.
Don’t let the word “molecular” scare you off. We give you details, but we break them down so that you can easily follow along. We track the progress of how your genes work from start to finish: how your DNA is put together, how it gets copied, and how the building plans for your body are encoded in the double helix.
Part 3, “Genetics and Your Health”:
Part 3
is intended to help you see how genetics affects your health and well-being. We cover the subjects of genetic counseling; inherited diseases; genetics and cancer; and chromosome disorders such as Down syndrome. We also include a chapter on gene therapy, a practice that may hold the key to cures or treatments for many of the disorders we describe in this part of the book.
Part 4, “Genetics and Your World”:
Part 4
explains the broader impact of genetics and covers some hot topics that are often in the news. We explain how various technologies work and highlight both the possibilities and the perils of each. We delve into population genetics (of both humans, past and present, and endangered animal species), evolution, DNA and forensics, genetically modified plants and animals, and the issue of ethics, which is raised on a daily basis as scientists push the boundaries of the possible with cutting-edge technology. To help you understand how scientists explore the secrets stored in your DNA, we also cover how DNA is sequenced. In the process, we relate the fascinating story behind the Human Genome Project.
Part 5, “The Part of Tens”:
In
Part 5
, you get our lists of ten of the next big things in the field and ten careers in genetics.
Foolish Assumptions
It's a privilege to be your guide into the amazing world of genetics. Given this responsibility, you were in our thoughts often while we were writing this book. Here’s how we imagine you, our reader:
You’re a student in a genetics or biology class.
You’re curious to understand more about the science you hear reported in the news.
You’re an expectant or new parent or a family member who’s struggling to come to terms with what doctors have told you.
You’re affected by cancer or some hereditary disease, wondering what it means for you and your family.
If any of these descriptions fit, you’ve come to the right place.
Icons Used in This Book
All For Dummies books use icons to help readers keep track of what’s what. Here’s a rundown of the icons we use in this book and what they all mean.
This icon points out stories about the people behind the science and accounts of how discoveries came about.
This icon flags information that’s critical to your understanding or that’s particularly important to keep in mind.
These details are useful but not necessary to know. If you’re a student, though, these sections may be especially important to you.
Points in the text where we provide added insight on how to get a better handle on a concept are found here. We draw on our personal experience for these tips and alert you to other sources of information you can check out.
This icon alerts you to concepts that are typically confusing to people new to the field of genetics. We help you avoid these common misunderstandings.
Beyond This Book
In addition to the abundance of information and guidance related to genetics that we provide in this book, you get access to the following help and information online at Dummies.com:
Cheat Sheet:
To access this book’s online Cheat Sheet, go to
www.dummies.com
and search for “Genetics For Dummies Cheat Sheet.”
Bonus chapters:
To access this book’s three bonus chapters, go to
www.dummies.com/go/geneticsfd4e
. You’ll find chapters about cloning and defining events in the genetics, as well as a handy online glossary.
Where to Go from Here
With Genetics For Dummies, 4th Edition, you can start anywhere, in any chapter, and get a handle on what you’re interested in right away. We make generous use of cross-references throughout the book to help you get background details that you may have skipped earlier. The table of contents and index can point you to specific topics in a hurry, or you can just start at the beginning and work your way straight through. If you read the book from front to back, you’ll get a short course in genetics in the style and order that it’s often taught in colleges and universities — Mendel first and DNA second.
Part 1
The Lowdown on Genetics: Just the Basics
IN THIS PART …
Discover the basics of genetics.
Explore how cells divide and separate their chromosomes.
Learn about Mendelian genetics and the fundamentals of how genes and traits are inherited.
Go beyond the fundamentals of inheritance to see how multiple genes can interact to determine your traits.
Chapter 1
Welcome to Genetics: Just About Everyone Loves a Good Pair of Genes
IN THIS CHAPTER
Defining the subject of genetics and its various subdivisions
Studying the genetics of individuals and families
Exploring DNA science through molecular genetics
Studying genetic diversity and its evolution within populations of a species
Examining how a trait can vary from one individual to another
Welcome to the complex and fascinating world of genetics. Genetics is all about physical traits and the DNA code that supplies the building plans for any organism. This chapter defines the field of genetics and explains what geneticists do. You get an introduction to the big picture and a glimpse at some of the details found in other chapters of this book.
Unwrapping Life’s Secrets
Take a moment to think about the vast diversity of living things in the world around you. The instructions to build all of those diverse forms — from a long, limbless snake to a tentacled octopus to a tall redwood tree — are encoded in the chemical pattern of DNA. Genetics is the field of science that examines how DNA determines traits and how these traits are passed from one generation to the next. Simply put, genetics affects everything about every living thing on earth. An organism’s genes are segments of DNA (deoxyribonucleic acid) that are the fundamental units of heredity. Genes play an essential role in how the organism looks, behaves, and reproduces. Because all biology depends on genes, genetics is a critical foundation for all other life sciences, including agriculture and medicine.
From a historical point of view, genetics is still a young science. The principles that govern inheritance of traits by one generation from another were described (and promptly lost) less than 150 years ago. Around the turn of the 20th century, the laws of inheritance were rediscovered, an event that transformed biology forever. Even so, it wasn’t until the 1950s that the importance of DNA was really understood. Now technology is helping geneticists push the envelope of knowledge every day.
Genetics is generally divided into four major subdivisions. We discuss each of these more in the sections that follow:
Classical, or Mendelian, genetics:
A discipline that describes how physical characteristics (traits) are passed along from one generation to another.
Molecular genetics:
The study of the chemical and physical structures of DNA, its close cousin RNA (ribonucleic acid), and proteins. Molecular genetics also covers how genes do their jobs.
Population genetics:
A division of genetics that looks at the genetic makeup of larger groups.
Quantitative genetics:
A highly mathematical field that examines the statistical relationships between genes and the traits with which they are associated.
In the academic world, many genetics courses begin with classical genetics and proceed through molecular genetics, with a nod to population and quantitative genetics. In general, this book follows the same path, because each division of knowledge builds on the one before it. That said, it’s perfectly okay, and very easy, to jump around among disciplines. No matter how you take on reading this book, it provides lots of cross-references to help you stay on track.
Classical Genetics: Studying How Traits Are Transmitted within Families
At its heart, classical genetics is the genetics of individuals and their families. It focuses mostly on studying physical traits, or phenotypes, as a way to understand the genes behind those traits.
Gregor Mendel, a monk and part-time scientist, founded the discipline of genetics. Mendel was a gardener with an insatiable curiosity to go along with his green thumb. His observations may have been simple, but his conclusions were jaw-droppingly elegant. This man had no access to technology, computers, or a pocket calculator, yet he determined, with keen accuracy, fundamental laws of inheritance that have stood the test of time.
Classical genetics is sometimes referred to as:
Mendelian genetics:
You start a new scientific discipline, and it gets named after you. Seems fair.
Transmission genetics:
This term refers to the fact that classical genetics describes how traits are passed on, or
transmitted,
from parents to their offspring.
No matter what you call it, classical genetics includes the study of cells and chromosomes, which we cover in Chapters 2 and 6. Cell division is the machine that drives inheritance, but you don’t have to understand combustion engines to drive a car, right? Likewise, you can dive straight into simple inheritance in Chapter 3 and work up to more complicated forms of inheritance in Chapter 4 without knowing anything whatsoever about cell division. (Mendel didn’t know anything about chromosomes and cells when he figured this whole thing out, by the way.)
The genetics of sex and reproduction are also part of classical genetics. Various combinations of genes and chromosomes (strands of DNA) determine biological sex. But the subject of sex gets even more complicated and interesting: The environment plays a role in determining the sex of some organisms (like crocodiles and turtles), and other organisms can even change sex with a change of address. If this has piqued your interest, you can find out all the astonishing details in Chapter 6. (Of note, we use the term sex throughout this book instead of the term gender. Sex is what defines males and females from a biological perspective. A person’s gender, on the other hand, may also be influenced by social and cultural factors, and may differ from one’s biological sex.)
Classical genetics provides the framework for many subdisciplines. The study of chromosome disorders such as Down syndrome, which we cover in Chapter 12, relies on cell biology and an understanding of what happens during cell division. Genetic counseling, which we cover in Chapter 14, also relies on understanding patterns of inheritance to interpret people’s medical histories from a genetics perspective. In addition, forensics, covered in Chapter 17, uses Mendelian genetics to determine paternity and to work out who’s who with DNA fingerprinting.
Molecular Genetics: Diving into DNA Science
Classical genetics concentrates on studying outward appearances, while the study of actual genes falls under the heady title of molecular genetics. The area of operations for molecular genetics includes all the machinery that runs cells and manufactures the structures called for by the plans found in genes. The focus of molecular genetics includes the physical and chemical structures of the double helix, DNA, which is broken down in all its glory in Chapter 5. The messages hidden in your DNA (your genes) constitute the building instructions for your appearance and everything else about you — from how your muscles function and how your eyes blink to your blood type, your susceptibility to particular diseases, and everything in between. How that DNA (and the immense amount of information it contains) is packaged in your cells is covered in Chapter 6, which reviews the structure and function of chromosomes.
Your genes are expressed through a complex system of interactions that begins with transcription — copying DNA’s messages into a somewhat temporary form called RNA, which is short for ribonucleic acid and is covered in Chapter 8. RNA carries the DNA message through the process of translation, covered in Chapter 9, which in essence is like taking a blueprint to a factory to guide the manufacturing process. Where your genes are concerned, the factory makes the proteins (from the RNA blueprint) that get folded in complex ways to make the various components of the cells and tissues in the human body. The study of gene expression (how genes get turned on and off, which we review in Chapter 10) and how the genetic code works at the levels of DNA and RNA are considered parts of molecular genetics.
Research on the causes of cancer and the hunt for better treatments, which we address in Chapter 13, focuses on the molecular side of things because tumors result from changes in the DNA, called mutations. Chapter 11 covers mutations in detail. Gene therapy, covered in Chapter 15, and genetic engineering, covered in Chapter 19, are subdisciplines of molecular genetics.
Population Genetics: Studying the Genetics of Groups
The science of genetics has a strong foundation in math. (In fact, Gregor Mendel studied to be a math teacher.) One area in which calculations are used to describe what goes on genetically is population genetics.
If you use Mendelian genetics and examine the inheritance patterns of many different individuals who have something in common, like geographic location, you can study population genetics. Population genetics is the study of the genetic diversity of a subset of a particular species (for details, you can flip ahead to Chapter 16). Basically, it’s a search for patterns that help describe the genetic signature of a particular group, such as the consequences of migration, isolation from other populations, and mating choices.
Population genetics helps scientists understand how the collective genetic diversity of a population influences the health of individuals within the population. For example, cheetahs are lanky cats; they’re the speed demons of Africa. Population genetics has revealed that all cheetahs are extremely genetically similar; in fact, they’re so similar that a skin graft from one cheetah would be accepted by any other cheetah. Because the genetic diversity of cheetahs is so low, conservation biologists fear that a disease could sweep through the population and kill off all the individuals of the species. It’s possible that no animals would be resistant to the disease, and therefore, none would survive, leading to the extinction of this amazing predator.
Evolutionary genetics is a type of population genetics that involves studying how traits change over time. We review evolutionary genetics in Chapter 16. Describing the genetics of populations from a mathematical standpoint is also critical to forensics, as explained in Chapter 17. To pinpoint the uniqueness of one DNA fingerprint, geneticists need to sample the genetic fingerprints of many individuals and decide how common or rare a particular pattern may be. Likewise, medicine uses population genetics to determine how common particular DNA changes are and to develop new medicines to treat disease (discussed in Chapter 15).
Quantitative Genetics: Exploring the Heredity of Complex Traits
Quantitative genetics examines traits that vary in subtle ways and relates those traits to the underlying genetics of an organism. A combination of whole suites of genes and environmental factors controls characteristics like retrieving ability in dogs, egg size or number in birds, and running speed in humans. Mathematical in nature, quantitative genetics takes a rather complex statistical approach to estimate how much variation in a particular trait is due to the environment and how much is actually genetic.
One application of quantitative genetics is determining how heritable a particular trait is. This measure allows scientists to make predictions about how offspring will turn out based on characteristics of the parent organisms. Heritability gives some indication of how much a characteristic (like seed production) can change when selective breeding (or, in evolutionary time, natural selection) is applied.
GREAT GENETICS WEBSITES TO EXPLORE
The Internet is an unparalleled source of information about genetics. With just a few mouse clicks, you can find the latest discoveries and attend the best courses ever offered on the subject. Here’s a quick sample.
To see a great video that explains genetics and gives it a human face, check out “Cracking the Code of Life”: https://www.pbs.org/wgbh/nova/genome/program.html.New discoveries are unveiled every day. To stay current, log on to www.sciencedaily.com/news/plants_animals/genetics and https://www.sciencenews.org/topic/genetics.For students, http://learn.genetics.utah.edu can't be beat. From the basics of heredity to virtual labs to cloning, it’s all there in easy-to-grasp animations and language.Want to get all the details about genes and diseases? Medline Plus provides straightforward explanations on numerous topics: https://ghr.nlm.nih.gov. You could also start at https://www.ncbi.nlm.nih.gov/books/NBK22183 for a review of the basics. More advanced (and greatly detailed) information is available at Online Mendelian Inheritance in Man (OMIM): www.ncbi.nlm.nih.gov/omim.If you’re interested in a career in genetics, the American Society for Human Genetics is ready to help: https://www.ashg.org/careers-learning/career-flowchart. (You can also check out some career descriptions in Chapter 22.)
