9781422280751

STEM: SHAPING THE FUTURE ARTIFICIAL INTELLIGENCE COMPUTING AND THE INTERNET

GENETIC ENGINEERING MEDICAL DISCOVERIES

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table of contents

Chapter 1: Introduction to Genetics

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Chapter 2: Biotechnology

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Chapter 3: Genetic Engineering in Humans Chapter 4: Genetically Modified Foods

27 41 55 63 74 76 77 78

Chapter 5: Cloning

Chapter 6: Business and Ethics in Genetic Engineering Series Glossary of Key Terms

Further Reading Internet Resources

Index

WORDS TO UNDERSTAND

centrifuge —a machine that uses spinning force, away from the center, to separate substances or parts of substances of different densities DNA —deoxyribonucleic acid: a molecule that carries genetic information in the cells of plants and animals gel electrophoresis —a process in which an electromotive force moves molecules (as proteins and nucleic acids) through a gel and separates them into bands according to size GMO —genetically modified organism: a plant or animal whose genetic material has been altered by genetic engineering genes —a part of a cell that controls or influences the appearance, growth, etc., of a living thing genetic engineering —the science of making changes to the genes of a plant or animal to produce a desired result selective breeding —the intentional mating of two animals or plants in an aempt to produce offspring with desirable characteristics or for the elimination of a trait

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HAVE YOU EVER WONDERED why you have blue eyes like your mother or why your sister’s hair is curly like your uncle’s? Many of our features are determined by genes —the parts of a cell that control the characteristics of a living thing—which we inherit from our parents and even grandparents. To put it simply, genes are bits of chemicals that are like instructions. They tell a living thing how to grow, survive, and carry out its life processes. Scientists are learning more and more about genetics, and with their growing knowledge comes the ability to change, or “engineer” genes to produce specific features— not only in people but in other species too. We can now work directly with genes, adding, chapte r INTRODUCTION TO GENETICS

removing, and modifying them to make the types of plants and animals we want. This is called genetic engineering or genetic modification. We can “cut and paste” genes within a single species or even between species—taking a gene from a fish and puing it into a plant cell, for example. In this book, we will look at how people are working with genetic information and think about some of the difficult but critical questions this science raises. There may be no “right” answers in many cases, but they are issues we must all consider if we are to play an effective role as citizens in the future of genetics. This book will not tell you what to think. It will give you some scientific background and present many different views and questions to consider. Then you can think about and discuss the issues, forming your own opinions which you will be able to explain and defend.

Many of your physical features are inherited—that’s why you share characteristics with other members of your birth family.

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GENETIC ENGINEERING IN NATURE People have bred animals and plants with desired features for many centuries. Farmers would pick the sheep with the thickest wool and breed from them, perhaps using the less-woolly sheep for food. They would gather seed from the strongest wheat plants to sow for the next crop. Choosing to breed from particular individuals in this way is called selective breeding . Historically, our farm animals and crops have been developed through centuries of selective breeding. But we now understand that the characteristics we want in a plant or animal are determined by its genes. We are learning which genes control which features in certain animals and plants. GENETICS BETWEEN GENERATIONS

All plants and animals have characteristics that they inherit from their parents. What they look like and how they work are passed on from one generation to the next. Some features are fixed for the species of plant or animal—all blackbirds have two legs and a beak, for example. But others vary between individuals—some spaniels are brown while others are white. The “recipe” for an individual plant or animal is carried in its genes. This includes information for the features that are always the same and for those that differ between individuals. Genes are passed on from one generation to the next through the process of reproduction. A living thing starts as one cell, which divides again and again to form more cells. Each time a cell divides, its genes are copied into the new cells. Not all your characteristics are coded in your genes; some come about as a result of how you are brought up, where you live, the type of diet you eat, the experiences you have had, and so on. These are called environmental factors. You may have the genes to grow tall, for instance, but if you are underfed, it may not happen. DNA AND GENES Imagine that you have to build a complex machine from thousands of parts. To fit them together, you need a set of instructions. A living organism is far more complicated than In the Middle Ages, hunting dogs were bred for their speed, strength and ability to track animals. Although no one understood how selective breeding worked, they made use of it to produce the animals they wanted.

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There’s nearly five feet (1.5 meters) of DNA in each of your cells—if you laid all the DNA in your body end to end it would reach to the sun (93 million miles) and back about 40 times! SIDEBAR

any machine. It has billions of parts that work together. Yet, it also needs a set of instructions, so it can grow, develop, and survive. The instructions for a machine are usually wrien on paper. Those for a living thing are in the form of a molecule called deoxyribonucleic acid ( DNA ), a sequence of codes that exists in every cell. In 1953, James Watson and Francis Crick discovered that DNA looks like a long ladder twisted into the shape of a corkscrew called a double-helix. The double-helix shape plays an important role in the way a gene is copied so that its product can be made.

If DNA is the “instruction book,” genes are like individual pages of the book that explain how to make specific parts of the machine: in the DNA sequence of codes, genes make up sections of that code sequence. A machine’s instructions are big enough for us to see, but genes are so

Gregor Mendel is considered the father of genetics. He was the first to show how characteristics could be passed on from one generation to another.

tiny they can only be seen by using special microscopes. All the genes for a living thing, from a daisy or worm to a tree or whale, are in pieces of DNA that could fit onto the period at the end of this sentence. HOW GENES WORK All living things are made of cells, which are like building blocks. Cells are so small that about 10,000 would fit inside this “o.” There are 37.2 trillion cells in a human body, but a gene section of DNA is even smaller than a cell. To a gene, a cell is like a gigantic “living factory.”

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Each DNA strand is made up of smaller pieces, or subunits called bases, which are joined together in a long row like beads on a necklace. In the same way that a word carries information by the order of its leers, DNA carries information by the order of its bases, which form a code. We use 26 different leers to make words, but DNA has only 4 different bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Genes make up sections of the DNA double helix, and each gene has hundreds or thousands of bases in sequence, so it can carry a huge amount of information. The whole set of human genes has 3.1 billion pairs of bases. For a gene to work, the order of its bases is copied into another substance very similar to DNA, called ribonucleic acid (RNA). The RNA then goes to another place inside the cell, where it carries out its job, almost like a person in a factory. It gathers together various substances or raw materials and fixes them together in the right order, following the instructions in the original gene. GENE PRODUCTS

DNA is composed of two long strands that make a double-helix shape, like a twisted ladder. The bases that make up the “le‡ers” for the code of genetic information are like the rungs of the ladder.

The result of this process is a product—a substance or protein in the body. An example is the substance that gives the eyes their color. In one person, the product is blue, so the eyes

are blue. We say that the person has the gene for blue eyes. In another person, the gene for eye color has a slightly different order of bases. This gives a brown product for brown eyes. A whole human body has about 19,000 different types of genes. Every tiny cell contains all of these genes. But in any single cell, only some of the genes are “switched on.” The rest are “switched off.” In the cells at the front of Chromosomes (shown highly magnified here) are arranged and inherited in pairsone from each parent. Humans have 23 pairs of chromosomes in every cell.

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the eye, the genes for eye color are “on” and make their product while other genes are “off” and make nothing. The fact that all the cells contain all the types of genes is very important in genetic engineering. GENETIC ENGINEERING Every plant or animal, such as an apple tree or a sheep, has a set of thousands of genes within its DNA which resembles tiny threads of pale jelly. This DNA can be taken out by chemical means. In genetic engineering, the DNA is split into shorter pieces, each of which is studied to see which particular genes it contains. Then a gene can be altered, moved, removed, or put into the DNA of another living thing. To obtain genes, you need just a tiny piece of a living thing such as a strand of hair, a flake of skin, or a flower petal. Even a tiny piece contains millions of cells, and every cell contains the full set of the living thing’s genes. The first step to identifying genes is to heat the cells with chemicals to make them release their contents. These are then spun around very quickly in a centrifuge machine (like a spin dryer), which separates them into different layers. The DNA layer is thin and pale and looks like damp coon. Its threads can be wound onto a glass rod. The long lengths of DNA are split into shorter ones by warming them with various proteins called restriction enzymes. These short fragments of DNA are identified by adding them to yet more proteins, puing them in a clear gel, and passing electricity through the gel. This makes various fragments move different distances along the gel. Called gel electrophoresis , this process creates a row of lines that look like a supermarket barcode. This identifies the DNA piece and so identifies the gene.

DNA “fingerprinting” may soon replace traditional fingerprints. Even a tiny sample of blood, skin or hair is enough for DNA testing to help us identify a criminal or victim.

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ADDING GENES TO LIVING THINGS The fragments of DNA are genes or parts of genes. Once identified for their properties, the genes can be added to the DNA of another living thing by using microscopic lifeforms called phages to “carry” them. The phages, which are a type of virus, are put in a flask with copies of the new gene. Some of them take the new gene into themselves. The phages are then added to other cells such as those of an animal. Phages are so small that they can get into a cell and add the new gene to it. The altered cell is then electrically stimulated to divide and make more cells like itself. As it divides and makes more cells, it can even be made to develop into a whole living thing called a transgenic lifeform or genetically modified organism ( GMO ). BENEFITS AND RISKS OF GENETIC ENGINEERING Suppose that scientists study a plant that grows many large seeds. They take out and identify the genes that make the seeds big and numerous. Then they add these genes into another type of plant, where they do not occur naturally. The genes work in their new “home,” and the second plant grows more and bigger seeds. If this plant is a farm crop, this process is, of course, very helpful to the farmer. But genetics is hugely complex. Things can go wrong and o©en do. The rewards may be great, but there could be dangers involved that we cannot even imagine until they happen. THE HUMAN GENOME ORGANIZATION In April 2003, scientists from the Human Genome Organization (HUGO) finished making the list of all the genetic material for a human being. This full set of genes is called the human genome. Bill Clinton, then president of the US, called it “the most wondrous map ever produced by mankind.” Tony Blair, Prime Minister of the United Kingdom (UK), said it was “a breakthrough that opens the way for massive advancement.” Though a major step was taken in genetics for humans, we still do not know exactly what every gene does or how it works.

SIDEBAR

BENEFITS OF GENETIC ENGINEERING FOR HUMANS • Learn about, prevent, and cure many diseases. • Find ways to help wounds heal more quickly. • Discover how we evolved.

• Understand the differences in characteristics between humans. • Identify people from small samples of tissue such as skin or blood.

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The information we gain from the human genome has helped us to understand how our bodies work. We can now determine whether or not someone is likely to get certain diseases and even prevent or cure some inherited conditions. ETHICAL QUESTIONS We can already cross-match DNA from tiny samples of body tissue—such as hair, blood, or skin—with the DNA of a known person. This can help us to identify victims of war, disaster, or crime and prove whether people are related to one another. With the possibility of knowing so much information about someone by studying their DNA, we face difficult questions about our own rights and what we should and should not do. Are we entitled to keep our own genetic information private? How will people be affected by knowing they are likely to develop a serious disease? Is it safe or right to make changes to the DNA of any species of plant or animal? Who owns and can make money from genetic information? You will have the chance to explore these and other ethical issues as you work through this book.

A gene is a length of DNA that codes for a specific protein, and is contained in the chromosomes that are part of each cell.

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TEXT DEPENDENT QUESTIONS

1. Explain the difference between DNA and genes. 2. Describe the steps involved in genetic engineering.

EDUCATIONAL VIDEO

Scan here to watch a video on the basics of genetics.

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