1. Chapter 5: Biotechnology
How can the genetic code be altered?
Lectures by Mark Manteuffel, St. Louis Community College

2. Biotechnology is producing improvements in agriculture.
5.11–5.13
Biotechnology is producing improvements in agriculture.
Insert section opener photo
Section 5.4 Opener
A scientist works with transgenic plants in a greenhouse.
Understanding a phenomenon is nice, but controlling it takes the satisfaction to an entirely new level.
This may explain why there is so much excitement surrounding the field of biotechnology, in which technology is used to modify organisms, cells, and their molecules to achieve practical benefits. 2

3. 5.11 What is biotechnology? Genetic engineering
Adding, deleting, or transplanting genes from one organism to another, to alter the organisms in useful ways
 The modern emphasis in biotechnology is on genetic engineering, the manipulation of organisms’ genetic material by adding, deleting, or transplanting genes from one organism to another. 3

4. How do you create a plant resistant to being eaten by insects
How do you create a plant resistant to being eaten by insects? Or a colony of bacteria that can produce human insulin?
Insert figure 5-24
(Figure 5-24 Five important tools and techniques of most biotechnology procedures):
1. Chop up the DNA from a donor organism that exhibits the trait of interest.
2. Amplify the small amount of DNA into more useful quantities.
3. Insert the different DNA pieces into bacterial cells or viruses.
4. Grow separate colonies of the bacteria or viruses, each containing a different inserted piece of donor DNA.
5. Identify the colonies that have received the DNA containing the trait of interest. 4

5. Step 1: Cut a section of DNA
Use of restriction enzymes to isolate a section of DNA (gene) and cut it. The enzymes bind to a particular section of DNA based on the sequence (4-8 bases).
Now let’s explore each step in more detail (Figure 5-25 Restriction enzymes are used to isolate a gene of interest).
1. Chopping DNA from a donor organism
To begin, researchers select an organism that has a trait they want to make use of, perhaps in developing a product. The researchers might want to produce human growth hormone in large amounts. Their first step would be to obtain human DNA and cut the DNA into smaller pieces. Cutting DNA into small pieces is a process that is done by restriction enzymes.
Restriction enzymes have a single function: When they encounter DNA, they cut it into small pieces. These enzymes evolved to protect bacteria from attack by viruses.
Upon encountering DNA from an invading virus, a restriction enzyme recognizes and binds to a particular sequence of four to eight bases on the invader’s DNA and cuts there, thus making it impossible for the virus to reproduce within the bacterial cell. Since all DNA has the same structure, these enzymes can cut DNA from any source as long as the specific four-eight base sequence is present (bacteria protect their own DNA by modifying it, or it would be cut up also). Dozens of different restriction enzymes exist, each of which cuts DNA at a different location. 5

6. Make numerous copies using PCR
Step 2: Amplify DNA
Make numerous copies using PCR
2. Amplifying DNA pieces into more useful quantities
In many situations, only a small amount of DNA will be available for analysis or some other biotechnology use. The polymerase chain reaction (PCR) is a laboratory technique that allows a tiny piece of DNA (perhaps one that has been cut from a larger piece by restriction enzymes or one that has been recovered from a crime scene) to be duplicated repeatedly, producing virtually unlimited amounts of it.
The process involves heating up the DNA of interest, causing the two strands to separate. Then, in the presence of enzymes and plenty of free nucleotides, the DNA is cooled. As it cools, an enzyme matches free nucleotides with their complementary bases on each of the single strands, and covalently links these nucleotides together to form a new single strand across from each original. The results is two complete double-stranded copies of the DNA of interest. This process of heating and cooling can be repeated again and again until there are billions of identical copies of the target sequence. 6

7. DNA my be inserted into a plasmid or other carrier
Step 3: Insert DNA
DNA my be inserted into a plasmid or other carrier
If the DNA is inserted into DNA from another organism the new organism is considered a transgenic organism.
3. Inserting foreign DNA into the target organism
In the human growth hormone example mentioned above, the researchers might want to transfer the human growth hormone gene into the bacterium E. coli, creating transgenic organisms.
To create a transgenic organism (that is, an organism with DNA inserted from a different species), researchers must physically deliver the DNA from a donor species into the recipient organism. This delivery often is accomplished using plasmids, circular pieces of DNA that can be incorporated into a bacterium’s genome (Fig. 5-27).
Genes on the plasmid can then be expressed in the bacterial cell and are replicated whenever the cell divides, so both of the new cells contain the plasmid. In some cases, for the delivery process, genes are incorporated into viruses instead of plasmids. The viruses can then be used to infect organisms and transfer the genes of interest into those organisms. 7

8. Step 4: Grow
Once a piece of foreign DNA has been transferred to a bacterial cell, every time the bacterium divides, it creates a clone, a genetically identical cell that contains that inserted DNA.
Insert figure 5-28
4. Growing bacterial colonies that carry the DNA of interest: Cloning
Once a piece of foreign DNA has been transferred to a bacterial cell, every time the bacterium divides, it creates a clone, a genetically identical cell that contains that inserted DNA. The term cloning describes the production of genetically identical cells, organisms, or DNA molecules, a process that occurs each time a bacterium divides. With numerous rounds of cell division, it is possible to produce a huge number of clones, all of which transcribe and translate the gene of interest.
In a typical experiment, a large amount of DNA may be chopped up with restriction enzymes, incorporated into plasmids, and introduced into bacterial cells. The bacteria are then allowed to divide repeatedly, with each producing a clone of the foreign DNA fragment they carry. Together, all of the different bacterial cells containing all of the different fragments of the original DNA are called a clone library or a gene library (Fig. 5-28). 8

9. Step 5: Identify
Once the cells are identified using a DNA probe, they can then be separated out and grown in large numbers—for example, vats of E. coli that produce human growth hormone.
Insert figure 5-29
5. Identifying bacterial colonies that have received the gene of interest
Chopping up human DNA and inserting the pieces (each of which carries different genes) into the genomes of bacteria, which divide repeatedly, leads to a large population of bacterial cells, with many carrying useful genetic information. But the information is in no particular order, much like a bookstore in which all the books are uncatalogued and in complete disarray. How can a researcher interested in working with bacterial cells that contain just the one human gene capable of producing human growth hormone identify and separate those bacteria from the other bacteria in the population?
Researchers have developed a way to make the bacteria of interest identify themselves (Fig. 5-29). First, a chemical is added to the entire population of bacterial cells, separating the double-stranded DNA into single strands. Next, a short sequence of single-stranded DNA is washed over the bacteria. Called a DNA probe, this DNA contains part of the sequence of the gene of interest and has also been modified so that it is radioactive. Bacteria with the gene of interest bind to this probe and glow with radioactivity. These cells can then be separated out and grown in large numbers—for example, vats of E. coli that produce human growth hormone. 9

10. Take-home message 5.11
The methods rely on naturally occurring restriction enzymes for cutting DNA, the polymerase chain reaction for amplifying small amounts of DNA, inserting the DNA into bacterial or viral vectors, and cloning and identifying the cells with the transferred DNA of interest. 10

11. 5.12 Biotechnology can improve food nutrition and make farming more efficient and eco-friendly.
Insert figure 5-30
For thousands of years, humans have been practicing a relatively crude and slow form of genetic engineering—the manipulation of a species’ genome in ways that do not normally occur in nature. In its simplest form, genetic engineering is the careful selection of the plants or animals used as the breeders for a crop or animal population. Through this process, farmers and ranchers have produced meatier turkeys, seedless watermelons, and big, juicy corn kernels (Fig. 5-30). But what used to take many generations of breeding can now be accomplished in a fraction of the time, using recombinant DNA technology, the combination of DNA from two or more sources into a product. 11

12. Nutrient-rich “golden rice”
How might a genetically modified plant help 500 million malnourished people?
Nutrient-rich “golden rice”
Almost ten percent of the world’s population suffers from vitamin A deficiency, which causes blindness in a quarter-million children each year and a host of other illnesses in people of all ages. These nutritional problems are especially severe in places such as southern Asia and sub-Saharan Africa where rice is a staple of most diets. Addressing this global health issue, researchers have developed what may be the model for solving problems with biotechnology. It involves the creation of a new crop, called “golden rice.” 12

13. Since golden rice was first developed in 1999, new lines have been produced with more than 25 times as much vitamin A than the original strains had.
Mammals generally make vitamin A from beta-carotene, a substance found in abundance in most plants (it’s what makes carrots orange). Beta-carotene is also found in rice plants, but not in the edible part of the rice grains. Researchers set out to change this by inserting into the rice genome three genes that code for the enzymes used in the production of beta-carotene. It’s clear that the transplanted genes are working because the normally white rice takes on a golden color from the accumulated beta-carotene. The rice doesn’t yet supply a full-day’s requirement of vitamin A in one serving but it does provide a significant amount. Since golden rice was first developed in 1999, new lines have been produced with more than 25 times as much vitamin A than the original strains had. Field tests of golden rice are still underway, so it is not yet being used widely but it is viewed as one of the most promising applications yet of biotechnology.
Figure 5-31 The potential to prevent blindness in 250,000 people each year. 13

14. What foods are responsible for this?
Almost everyone in the United States consumes genetically modified foods regularly without knowing it. What is different about Connecticut?
What foods are responsible for this?
Currently, more than 170 million acres worldwide are planted with genetically modified crops, most containing built-in insecticides and herbicide resistance, representing more than a forty-fold increase over the past 10 years. The financial benefits to farmers—at least in the short run—are so great that more and more of them are embracing the genetically modified crops.
The numbers are surprising: 86% of all corn grown in the United States is genetically modified. Ninety-three percent of all cotton grown is genetically modified. And 93% of all soybeans grown are genetically modified (Fig. 5-32). Two factors explain much of the extensive adoption of genetically modified plants in U.S. agriculture. (1) Many plants have had insecticides engineered into them, which can reduce the amounts of insecticides used in agriculture. (2) Many plants also have herbicide-resistance genes engineered into them. Such herbicide-resistant plants as
well as insect-resistant plants can reduce the amount of plowing required around crops to remove weeds. As a consequence, then, the use of genetically modified plants can reduce both the costs of producing food and the loss of topsoil to erosion. 14

15. Insect Resistance – Toxic Bt crystals spryaed on plants
Insert figure 5-33
Insect pests have a field day on agricultural crops (Figure 5-33 Competing with us for food). Crops—whether cotton, potatoes, peas, or something else—that are planted at high densities and nurtured with ample water and fertilizer represent a huge potential food resource for insects. Every year about 40 million tons of corn are unmarketable as a consequence of insect damage. Increasingly, however, farmers have been enjoying greater success in their battles against insect pests, primarily through the use of transgenic crops.
Farmers owe much of this success to soil-dwelling bacteria of the species Bacillus thuringiensis. These bacteria produce spores containing crystals that are highly poisonous to insects but harmless to the crop plants and people. Within an hour of ingesting the crystals, the insect’s feeding is disrupted. The toxic crystals cause pores to develop throughout the insects’ digestive system, paralyzing their gut and making them unable to feed. Within a few days the insects die from a combination of tissue damage and starvation. 15

16. How can genetically modified plants lead to reduced pesticide use by farmers?
Beginning in 1961, the toxic “Bt” crystals were included in pesticides that were sprayed on plants. In 1995, however, recombinant DNA technology led to a huge improvement. The gene coding for the production of the Bt crystals was inserted directly into the DNA of many different crop plants, including corn, cotton, and potatoes, so that the plants themselves produced the crystals. 16

17. As a consequence, it is no longer necessary for farmers to apply huge amounts of Bt-containing pesticides (Figure 5-34 Help from bacteria in growing disease-resistant corn). Instead, the plants do that work themselves. The insects that try to eat the genetically modified plants ingest the toxin and soon die. There is no evidence that Bt crystals have any harmful effects on humans at all, even when they are exposed to very high levels. 17

18. Herbicide Resistance
Bacteria have come to the aid of farmers fighting pests in another way, too. Consider a seemingly impossible challenge the farmers face when they attempt to kill weeds that harm crop plants by competing for light, water, and soil nutrients. Herbicides, chemicals that kill plants, can be applied to kill the weeds. These chemicals usually work by blocking the action of an enzyme that enables plants, fungi, and bacteria to build three critical amino acids. Without these amino acids, the organisms soon die. The problem is that because the herbicides affect all plants similarly, they are generally toxic to the crop plant as well as the weeds. This is where bacteria come in.
In the 1990s, researchers discovered bacteria that can resist the effect of the herbicide and build the three amino acids even in the presence of the herbicide. The gene that gives the bacteria resistance to herbicides was identified and introduced into crop plants. Integration of this gene into the plants’ DNA gives them resistance to the herbicides and allows farmers to kill weeds with herbicides without harming the crop plants, greatly increasing yields (Figure 5-35 Crop duster). 18

19. Faster Growth and Bigger Bodies - Article and discuss
Agriculture includes not just the cultivation of plants but also of animals. Currently, researchers have been developing transgenic salmon that grow significantly faster and much larger than normal salmon (Figure 5-36 Bigger salmon). The salmon carry a version of the growth hormone gene that functions year round, rather than primarily in the summer. It was isolated from a cold-water fish species, called Arcticpout, and injected into the egg of a salmon. The super-fish can be raised much more quickly and uses significantly less feed than normal salmon, reaching market size within 18 months, rather than the usual 24–30 months. In taste tests, consumers cannot tell the difference between the transgenic and non-transgenic salmon.
Quite troubling is the fact that researchers expected growth rate increases of about 25% but found that the genetically modified fish grew about 500% faster. Additionally, if the larger, faster-growing fish escaped from their breeding nets back into their natural habitat—something that experts agree is inevitable—the fish might harm populations of other species because they can consume more of their own prey and because they may grow too large to be consumed by their natural predators. It is unclear what the outcome would be. 19

20. Take-home message 5.12
Even more significant is the extent to which biotechnology has reduced the environmental and financial costs of producing food:
Through the creation of herbicide-resistant and insect-resistant crops 20

21. Take-home message 5.12
The ecological and health risks of such widespread use of transgenic species are not fully understood and are potentially great. 21

22. 5.13 Fears and risks: Are genetically modified foods safe?
Chickens without feathers look ridiculous (Figure 5-37 “Naked” birds). But such a genetically modified breed was developed with a valuable purpose in mind: “Naked” birds are easier and less expensive to prepare for market, benefiting farmers by lowering their costs and consumers by lowering prices. Such chickens, however, turned out to be unusually vulnerable to mosquito attacks, parasites, and disease, and ultra-sensitive to sunlight. They also have difficulty mating since the males are unable to flap their wings. Researchers currently are working to address these problems.
These chickens teach us an important lesson about genetically modified plants and animals. Although the new breed of featherless chickens was produced by traditional animal husbandry methods—the cross-breeding of two different types of chickens—as opposed to using recombinant DNA technology, the new breed ended up having not just the desired trait of no feathers, but it also had some unintended and undesirable traits. 22

23. Fear #1. Organisms that we want to kill may become invincible.
Fear #2. Organisms that we don’t want to kill may be killed inadvertently.
Fear #3. Genetically modified crops are not tested or regulated adequately.
Now as more genetically modified foods are created using modern methods of recombinant DNA technology, the same risks of unintended and potentially harmful traits occurring must be weighed. For these and other reasons—some legitimate and rational, others irrational—many people have concerns about the production and consumption of genetically modified foods (Figure 5-38 Consumer fears).
Fear #1. Organisms that we want to kill may become invincible.
Weed-resistant canola plants were cultivated in Canada, making it possible for farmers to apply herbicides freely to kill the weeds but not the canola plants. But the weed-resistant canola plants accidentally spread to neighboring farms and grew out of control because traditional herbicides could not kill them.
Fear #2. Organisms that we don’t want to kill may be killed inadvertently.
Monarch butterflies feed on milkweed plants. Recent research has demonstrated that if pollen from genetically modified plants containing the insect-killing Bt genes accidentally lands on milkweed plants and is consumed by monarch butterflies, the butterflies can be killed, with significant effect on their populations. Although such an incident has not occurred, it illustrates a risk that may be hard to control.
Fear #3. Genetically modified crops are not tested or regulated adequately.
It is impossible to ever really know whether a new technology has been tested adequately. Still, scientists have been working toward an organized and responsible set of policies designed to insure sufficient safety-testing is done. Guidelines have been developed and established as formal government regulations in the United States and some other countries. For example, laboratory procedures for working with recombinant DNA have been established and researchers have developed techniques that make it impossible for most genetically engineered organisms to survive outside the specific conditions for which they are developed.
As an example of the degree of testing used in the field of genetically engineered foods, the Monsanto Company has had their strain of herbicide-resistant soybeans evaluated and approved by 31 different regulatory agencies in 17 different countries, including the U.S. Department of Agriculture, the Food and Drug Administration, and the Environmental Protection Agency in the United States. In a recent report on genetically modified animals, however, an expert committee from the U.S. National Academy of Sciences warned that the bio-engineered organisms still pose risks that the government is unable to evaluate. Technology is moving so fast that it is difficult to even know what the new risks might be. 23

24. Fear #4. Eating genetically modified foods is dangerous
Fear #5. Loss of genetic diversity among crop plants is risky.
Fear #6. Hidden costs may reduce the financial advantages of genetically modified crops.
Now as more genetically modified foods are created using modern methods of recombinant DNA technology, the same risks of unintended and potentially harmful traits occurring must be weighed. For these and other reasons—some legitimate and rational, others irrational—many people have concerns about the production and consumption of genetically modified foods.
Fear #4. Eating genetically modified foods is dangerous.
In the 1990s, a gene from Brazil nuts was used to improve the nutritional content of soybeans. The genetically modified soybeans had better nutritional content, but they also acquired some allergy-causing chemicals that previously had been present in the Brazil nuts but not the soybeans. This outcome illustrated the risk that some unwanted features may be passed from species to species in the creation of transgenic organisms. In this case, all of the genetically modified soybeans were destroyed and this research program was suspended. To date no evidence has appeared to suggest that consumption of any genetically modified foods is dangerous.
Fear #5. Loss of genetic diversity among crop plants is risky.
As increasing numbers of farmers stop using non-genetically modified crops in favor of one or a few genetically modified strains of crops, there is a reduction in the genetic diversity of the crops. This can make them more vulnerable to environmental changes or pests. Example: Irish potato famine of 1880s.
Fear #6. Hidden costs may reduce the financial advantages of genetically modified crops.
When seed companies create genetically modified seeds with crop traits desirable to farmers, the companies also engineer sterility into the seeds. As a consequence, the farmers must purchase new seeds for each generation of their crops. Such increases in the long-term costs and dependency on seed companies must be factored in by farmers.
Among the less rational fears is that GM foods are not “natural.” This fear should not be cause for concern. Small pox, HIV, poison ivy, and cyanide, after all, are natural. The small pox vaccine, on the other hand, is unnatural. Innumerable other valuable technological developments are equally unnatural. There simply is no value in knowing whether something is natural or unnatural when evaluating whether it is good and desirable. 24

25. for improving human health (and criminal justice)
5.14–5.17
Biotechnology
has the potential
for improving human health (and criminal justice)
Section 5.6 Opener
With the cloning of a sheep, a new era in biotechnology began.

26. 5.14 The treatment of diseases and production of medicines are improved with biotechnology.
Preventing diseases
Curing diseases
Treating diseases
The treatment of diabetes
You can’t always get what you want. In the best of all worlds, biotechnology would prevent humans from ever getting debilitating diseases. Next best would be to cure diseases once and for all. But these noble goals are not always possible, so biotechnology often is directed at the more practical goal of treating diseases, usually by producing medicines more efficiently and more effectively than they can be produced with traditional methods.
Biotechnology has achieved some notable successes in achieving this goal.
The treatment of diabetes is one such success story. 26

27. Insert figure 5-39
Diabetes is a chronic disease in which the body cannot produce the chemical insulin, which breaks down sugar in the blood. Complications from diabetes can include vascular disease, kidney damage, and nerve damage. As recently as 1980, if you were one of the approximately 15 million Americans with diabetes, each day you would treat the disease by injecting yourself with insulin extracted from the pancreas of cattle or pigs that had been killed for meat. For most diabetics, the insulin injections kept the disease under control. But the traditional process of collecting insulin this way was difficult and costly.
Everything changed in 1982 when a 29-year-old entrepreneur, Bob Swanson, joined scientist Herbert Boyer to transform the potential of recombinant DNA technology. In doing so, they started the biotech revolution. Working with the scientist Stanley Cohen, Swanson and Boyer used restriction enzymes to snip out the human DNA sequence that codes for the production of insulin. They then inserted this sequence into the bacterium E. coli, creating a transgenic organism. After cloning the new, transgenic bacteria, the team was able to grow vats and vats of the bacterial cells, all of which churned out human insulin (Fig. 5-39). The drug could be produced efficiently in huge quantities and made available for patients with diabetes. This was the first genetically engineered drug approved by the Food and Drug Administration and it continues to help millions of people every day.
Perhaps even more significant than providing a better source of insulin, Swanson, Boyer, and Cohen’s application of biotechnology revealed a generalized process for genetic engineering. It instantly opened the door to a more effective method of producing many different medicines and treating diseases. Today, more than 1500 companies work in the biotechnology industry, and their products generate more than $40 billion in revenues each year. 27

28. Human growth hormone (HGH)
Several important achievements followed the development of insulin-producing bacteria, including:
Human growth hormone (HGH)
Erythropoietin (EPO – increase RBCs -oxygen transport)
Several important achievements followed the development of insulin-producing bacteria. Two of these include:
1. Human growth hormone (HGH): Produced by the pituitary gland, growth hormone has dramatic effects throughout the body. It stimulates protein synthesis, increases utilization of body fat for energy to fuel metabolism, and stimulates the growth of virtually every part of the body (Figure 5-27 Bulking up with a little (illegal) help). Insufficient growth hormone production, usually due to pituitary malfunctioning, leads to dwarfism.
When treated with supplemental HGH, individuals with dwarfism experience additional growth. HGH is also used to combat weight loss in AIDS patients. Until 1994, it was prohibitively expensive because it could only be produced by extracting and purifying it from the pituitary glands of human cadavers. Through the creation of transgenic bacteria, using a technique similar to that used in the creation of insulin-producing bacteria, human growth hormone can now be created in virtually unlimited supplies and made available to more people who need it.
The availability of human growth hormone, which can increase strength and endurance, may be irresistibly tempting to some athletes—even at $7,500 for a month's supply. Recent sporting scandals suggest that the illegal use of HGH occurs frequently among elite swimmers, cyclists, and other athletes.
2. Erythropoietin: Produced primarily by the kidneys, erythropoietin (also known as EPO) regulates the production of red blood cells. Numerous clinical conditions (such as nutritional deficiencies and lung disease, among others) and treatments (such as chemotherapy) can lead to anemia, a lower than normal amount of red blood cells, which reduces an individual’s ability to transport oxygen to tissues and cells.
Cloned in 1985, recombinant human erythropoietin (rhu-EPO) is now produced in large amounts in hamster ovaries. It is used to treat many forms of anemia. Worldwide sales of EPO exceeded $10 billion in 2004. 28

29. How does it improve some athletes’ performance?
What is “blood doping”?
How does it improve some athletes’ performance?
EPO (Erythropoietin) has been at the center of several “blood doping” scandals in professional cycling. This hormone increases the oxygen-carrying capacity of the blood, so some otherwise healthy athletes have used EPO to improve their athletic performance. It can be very dangerous, though. By increasing the number of red blood cells, the blood can become much thicker and this can increase the risk of heart attack. 29

30. But has had a limited success in curing them
5.15 Gene therapy: Biotechnology can help diagnose and prevent diseases.
But has had a limited success in curing them
Class ethical discussion
Would you want to know? Once this was just a hypothetical question: If you carried a gene that meant you were likely to develop a particular disease later in your life, would you want to know? Or another question: Would you want to know if a baby that you and your spouse were trying to conceive would be born with a genetic disease? Now, for better or for worse, these are becoming real questions that we all must address. And there is more at stake than simply peace of mind. As biotechnology develops the tools to identify some of the genetic time-bombs that many of us carry, it also carries the danger that such information may become the basis for greater discrimination than we have ever known. 30

31. 1. Is a given set of parents likely to produce a baby with a genetic disease?
Insert figure 5-41
Intervening to prevent diseases using biotechnology focuses on answering questions at three different points in time:
1. Is a given set of parents likely to produce a baby with a genetic disease?
Many genetic diseases occur only if an individual inherits two copies of the disease-causing gene, one from each parent. This is true for Tay-Sachs disease, cystic fibrosis, and sickle-cell anemia, among others. Individuals with only a single copy of the disease-causing gene never fully manifest the disease but may pass on the disease gene to their children. Consequently, two healthy parents may produce a child with the disease. In these cases, it can be beneficial for the parents to be screened to determine whether they carry a disease-causing copy of the gene. Such screening, combined with genetic counseling and testing of embryos following fertilization, can reduce the incidence of the disease dramatically. This has been the case with Tay-Sachs disease, for example. Since screening begin in 1969, the incidence of Tay-Sachs disease has been reduced by more than 75% (Figure 5-41 Genetic screening can determine the presence of the Tay-Sachs gene). 31

32. 2. Will a baby be born with a genetic disease?
Cystic fibrosis
Sickle-cell anemia
Down syndrome
Others
2. Will a baby be born with a genetic disease?
Once fertilization has occurred, it is possible to test an embryo or developing fetus for numerous genetic problems. Prenatal genetic screening can detect disorders such as cystic fibrosis, sickle-cell anemia, Down syndrome, and others. The list of additional conditions that can be detected is growing quickly.
To screen the fetus, it is necessary to sample some of the fetal cells and/or the amniotic fluid, which carries many chemicals produced by the developing embryo. This is usually done via amniocentesis or chorionic villus sampling (CVS)—techniques that we explore in detail in Chapter 6. Once collected, the cells can be analyzed using a variety of means. 32

33. 3. Is an individual likely to develop a genetic disease later in life?
Breast cancer
Prostate cancer
Skin cancer
3. Is an individual likely to develop a genetic disease later in life?
DNA technology can also be used to detect disease-causing genes in individuals that are currently healthy but are at increased risk of developing an illness later. Early detection of many diseases such as breast cancer, prostate cancer, and skin cancer can greatly enhance the ability to treat the disease and reduce the risk of more severe illness or death. 33

34. Boy in the Bubble – Severe Combined Immunodeficiency Syndrome (SCID) – GENE THERAPY
Insert figure 5-42
When it comes to curing a disease by using biotechnology, there is good news and bad news. The good news is that, in the 1990s, a handful of humans with a usually fatal genetic disease called severe combined immunodeficiency disease (SCID) were completely cured through the application of biotechnology. The bad news is that it has not been possible to apply these promising techniques to other diseases.
Let’s examine the case of SCID, which has served as a model for gene therapy. SCID is a condition in which a baby is born with an immune system unable to properly produce a type of white blood cell. This leaves the infant vulnerable to most infections and usually leads to death within the first year of life (Fig. 5-42). In gene therapy for SCID, researchers removed from an affected baby’s bone marrow some stem cells, cells that have the ability to develop into any type of cell in the body. In bone marrow, they normally produce white blood cells, but in individuals with SCID, a malfunctioning gene disrupts normal white blood cell production.
Next, in a test tube, the bone marrow stem cells were infected with a transgenic virus carrying the functioning gene. Ideally, the virus inserted the good gene into the DNA of the stem cells, which were then injected back into the baby’s bone marrow. There, the cells could produce normal white blood cells, permanently curing the disease. Although this strategy worked to cure several cases of SCID, treatment has been suspended indefinitely following the recent deaths of two patients from illness related to their treatment. 34

35. Difficulties with gene therapy have been encountered in several different areas, usually related to the organism used to transfer the normal-functioning gene into the cells of a person with a genetic disease.
Difficulties with gene therapy have been encountered in several different areas, usually related to the organism used to transfer the normal-functioning gene into the cells of a person with a genetic disease. 35

36. 5.16 Cloning—producing an identical copy
Cloning. Perhaps no scientific word more easily conjures horrifying images of the intersection of curiosity and scientific achievement. But is fear the appropriate emotion to feel about this burgeoning technology? Perhaps not.
For starters, let’s clarify what the word means. Cloning actually refers to a variety of different techniques. To be sure, cloning can refer to the creation of new individuals
that have exactly the same genome as the donor individual—a process called “whole organism cloning.” That is, a clone is like an identical twin, except that it may
differ in age by years or even decades. It is also possible to clone tissues (such as skin) and entire organs from an individual’s cells. And, as we saw in Section 5.11, it is possible to clone genes. 36

37. In 1997, Ian Wilmut, a British scientist, and his colleagues first reported that they had cloned a sheep—which they named Dolly.
Cloning took center stage in the public imagination in 1997, when Ian Wilmut, a British scientist, and his colleagues first reported that they had cloned a sheep—which they named Dolly. Their research was based on ideas that went back to 1938, when Hans Spemann first proposed the experiment of removing the nucleus from an unfertilized egg and replacing it with the nucleus from the cell of a different individual. Although the process used by Wilmut and his research group was difficult and inefficient, it was surprisingly simple in concept (Fig. 5-43). They removed a cell from the mammary gland of a grown sheep, put its nucleus into another sheep’s egg from which the nucleus had been removed, induced the egg to divide, and transplanted it into the uterus of a surrogate mother sheep. Out of 272 tries, they achieved just one success. But that was enough to show that the cloning of an adult animal was possible. 37

38. 5.17 DNA as an individual identifier: the uses and abuses of DNA fingerprinting
In another time, Colin Pitchfork, a murderer and rapist, would have walked free (Figure 5-45 Betrayed by his DNA). But in 1987, he was captured and convicted, betrayed by his DNA, and is now serving two life sentences in prison. Pitchford’s trouble began when he raped and murdered two 15-year-old high school girls in a small village in England in the 1980s. The police thought they had their perpetrator when a man confessed, but only to the second murder. He denied any involvement with the first murder, though, which perplexed the police because the details of the two crimes strongly suggested that the same person committed both.
At the time, British biologist Alec Jeffreys made the important discovery that there were small pieces of DNA within every person’s chromosomes that were tremendously variable in their base sequences. In much the way each person has a driver’s license or Social Security number that differs from everyone else’s, these DNA fragments are variable enough that it is extremely unlikely that two people would ever have identical sequences at these locations. Thus, a comparison between these regions in a DNA sample from a person and in evidence left at a crime scene would enable police to determine that the evidence came from that person.
Dr. Jeffreys analyzed DNA left by the murderer/rapist on the victims and found that it did indeed come from a single person, and that that person was not the man who originally confessed. That original suspect was released and has the distinction of being the first person cleared of a crime due to DNA fingerprinting. To track down the criminal, police then requested blood samples of all men in the area who were between 18- and 35-years-old, collecting and analyzing more than 5,000 blood samples. This led them to Colin Pitchfork, whose DNA matched perfectly the DNA left on both of the victims, and ultimately was the evidence responsible for his conviction. (He almost slipped through, having persuaded a friend to give a blood sample in his name. But when the friend was overheard telling the story in a pub, police tracked down Pitchfork to get a blood sample.) 38

39. What is a DNA fingerprint?
For each STR locus analyzed, an individual’s genotype is determined b using PCR to amplify that region, then measuring the length of the STR region using electrophoresis. The length of the region can then be used to determine the number of times that the STR is repeated. For a single STR region, an individuals’ genotype is two numbers, reflecting the number of STR repeats in the copies inherited from the mother and from the father. And a person’s full DNA fingerprint is a string of 26 numbers that includes the two numbers for each of 13 STRs.
In court, a suspect’s genotype might be compared with the DNA fingerprint obtained from evidence found at the crime scene. DNA samples from different people will produce different 26-number “fingerprints,” whereas different samples of DNA from one person will have exactly the same genotype (Fig. 5-47). 39

40. Insert figure 5-45c
DNA fingerprinting is now used extensively in forensic investigations, in much the same way that regular fingerprints have been used for the past 100 years. But traditional fingerprinting is limited in its usefulness for many crimes because no actual fingerprints are left behind. DNA fingerprinting, on the other hand, is not so limited because DNA samples more frequently are left behind, usually in the form of semen, blood, hair, skin, or other tissue. As a consequence, this technology has been directly responsible for bringing thousands of criminals to justice and, perhaps as importantly, for establishing the innocence of more than 200 people who were wrongly convicted of murder and other capital crimes. Let’s examine how DNA fingerprinting is done, why it is such a powerful forensic tool, and why it is not foolproof. 40