Deciphering Human Genetics
BY AWAKE! CORRESPONDENT IN BRITAIN
“BIOLOGY’S first ‘big science’ project,” sixth of “the seven wonders of the modern world”—both of these are descriptions of the Human Genome Project, an international attempt to decipher you! What is a genome? It is the sum total of your genetic makeup, one part inherited from your father and the other part from your mother but now uniquely yours.
Geneticists Sir Walter Bodmer and Robin McKie dub the genome project “the Book of Man.” But reading it is no simple task. “A more important set of instruction books will never be found by human beings,” claims James Watson, one of the scientists credited with discovering the structure of the now famous DNA molecule. “When finally interpreted,” he says, “the genetic messages encoded within our DNA molecules will provide the ultimate answers to the chemical underpinnings of human existence.”
As with any big and expensive science project, the Human Genome Project has both believers and skeptics. “The Genome Project could be the ultimate violation of privacy,” warns science writer Joel Davis, “or it could be an extraordinary doorway to renewed life, to health, to healing.” But whatever it achieves, he believes that “it will utterly change the field of genetics” and that “it may totally reshape the nature of Homo sapiens.” Back in 1989, George Cahill, a vice president at the Howard Hughes Medical Institute, was positive. “It’s going to tell us everything,” he said. “Evolution, disease, everything will be based on what’s in that magnificent tape called DNA.”
A Mammoth Task
In 1988 an international group of scientists set up HUGO (Human Genome Organization) to coordinate the work of genome researchers in participating countries. With a budget of some $3.5 billion, HUGO channels their results into a computer data base. Although computers now read thousands of its components every day, the genome is so complex that scientists do not expect to complete its decoding until sometime in the 21st century. Scientific American magazine estimates that if the genome were published in book form, it would take “a third of a lifetime” to read it through.
After much debate scientists decided on the following strategy. First, they intend to map the genome to locate the position of the 100,000 genes. Next, by a process known as sequencing the genome, they hope to discover the order of the building blocks that make up each of these genes. Their final goal is to sequence the other 95 to 98 percent of our genetic material.
Will achieving all of this reveal everything there is to know about human life? Does the genome contain ‘the most important set of instruction books’ man has ever found? Will the Human Genome Project spell out cures for all human ills? The following articles consider these questions.
What Makes You “You”
BEFORE the Human Genome Project began, scientists had learned much about our genetic makeup. That is why terms such as “genes,” “chromosomes,” and “DNA” frequently appear in news reports as the press announces discovery after discovery of what researchers believe make us what we are. The Human Genome Project now attempts to build on these basics and to read our whole genetic code.
Before we consider how scientists go about this, please read the box “Your Blueprint,” on page 6 of this magazine.
Locating the Genes
As mentioned in the preceding article, the first aim of the Human Genome Project has been to discover where our genes are located on our chromosomes. One gene hunter likens this to “searching for a burnt-out light bulb in a house with no address in an unknown street in an anonymous city in a foreign country.” Time magazine claims that the task is “as difficult as locating a phone number without an address or a last name.” How, then, do scientists tackle this challenge?
Researchers study families to locate the genes that determine characteristics that are inherited with well-known traits and susceptibilities. For example, they have traced genes for color blindness, hemophilia, and cleft palate to areas on one of our chromosomes. These genetic-linkage maps, as they are called, are very rough—they indicate the gene’s location only to within about five-million pairs of bases.
For more precision, scientists intend to compile a physical map. In one method, they break copies of the DNA into randomly sized pieces that they then survey for special marker sequences. Of course, the more pieces there are, the more difficult it is to sort them. If you compare each DNA fragment to a book on a clearly marked library shelf, then locating a gene resembles “finding a quote in a single book rather than having to search through a whole library,” explains New Scientist magazine. These physical maps narrow the search to within 500,000 base pairs. Toward the end of 1993, a team of scientists led by Dr. Daniel Cohen at the Center for the Study of Human Polymorphism in Paris, France, produced what Time magazine called “the first full-fledged—if still rough—map of the human genome.”
The project’s next goal is to list the exact sequence of the chemical components of each of our 100,000 genes, as well as the other parts of the genome. But as scientists develop their DNA-reading skills, they find the genome to be more complex than they envisaged.
Reading the Genome
Genes account for a mere 2 to 5 percent of our genome. The rest is often termed “junk DNA.” Some researchers once thought these so-called useless sequences accidentally developed during evolution. Now they believe that some of these nongene regions regulate the structure of DNA and contain instructions the chromosomes need in order to copy themselves during cell division.
Researchers have long been interested in what switches a gene on and off. New Scientist reports that there could be as many as 10,000 of our genes that code for the production of proteins called transcription factors. Several of these apparently join together and then fit into a groove in the DNA like a key in a lock. Once in place they either spark the nearby gene into action or suppress its function.
Then, there are so-called stuttering genes that contain multiple repeats of parts of the chemical code. One of these normally contains between 11 and 34 repeats of the CAG triplet—a sequence of three nucleotides that identifies a particular amino acid. When it has 37 or more repeats, it provokes a degenerative brain disorder called Huntington’s chorea.
Consider also the effect of the change of a letter in a gene. A wrong letter in the 146-letter sequence of one of the two components of hemoglobin causes sickle-cell anemia. Even so, the body has a proofreading mechanism that checks on the integrity of the DNA when cells divide. One fault in this system reportedly can cause colon cancer. Many other disorders, such as diabetes and heart disease, though not simply the result of a single genetic fault, nevertheless result from the combined action of many faulty genes.
Rewriting the Genome
Doctors look to the Human Genome Project for information that will help them to diagnose and treat man’s ills. Already they have developed tests that reveal abnormalities in certain gene sequences. Some worry that unscrupulous people will use genetic testing to carry out a policy of eugenics. Presently most oppose germ-line therapy, which involves altering the genes in sperm and in egg cells. Even couples who contemplate in vitro fertilization of a genetically normal embryo have to face decisions about what happens to those embryos not selected for reimplantation. Additionally, thinking people voice concerns about the consequences to the unborn of a diagnosis that reveals an apparent genetic fault. Fear that genetic mapping of adults will change the way they are employed, promoted, and even insured worries many. Then there is the vexing question of genetic engineering.
“Not satisfied with reading the book of life,” comments The Economist, “they want to write in it as well.” One way doctors may be able to do this is by using retroviruses. A virus can be thought of as a group of genes in a chemical bag. Starting with a virus that affects humans, scientists remove the genes the virus needs to reproduce itself and replace these with a healthy version of the patient’s faulty genes. Once injected into the body, the virus penetrates the target cells and replaces the faulty genes with the healthy ones it carries.
Based on the discovery of a gene that can give protection against skin cancer, scientists recently reported a simple treatment. Since only 1 person in 20 carries this gene, the aim is to include it in a cream that will insert this gene into skin cells. There the gene triggers production of an enzyme that doctors believe breaks down cancer-causing toxins that attack the body.
Marvelous as these procedures are, strict controls limit the use of genetic engineering as scientists battle public anxieties over its possible consequences.
Much remains to be discovered about the intricacies of the human genome. Indeed, “there is no single human genome,” notes geneticist Christopher Wills. “There are five billion of them, one for virtually every human being on the planet.” Your genome reveals much about you. But does it tell all?
Does Your Genome Reveal All?
Some believe that genes are little dictators that make us behave as we do. In fact, recent press reports have announced the discovery of genes that some believe are responsible for schizophrenia, alcoholism, and even homosexuality. Many scientists advise caution on these possible links. For example, author Christopher Wills writes that in some cases gene variants simply “predispose their carriers towards alcoholism.” According to The Times of London, molecular geneticist Dean Hamer expressed the view that human sexuality was much too complex to be determined by one gene. Indeed, the 1994 Britannica Book of the Year reports: “No specific gene was identified as predisposing to homosexuality, however, and the work done thus far would have to be confirmed by others.” Moreover, Scientific American magazine notes: “Behavioral traits are extraordinarily difficult to define, and practically every claim of a genetic basis can also be explained as an environmental effect.”
Interestingly, in the BBC television series Cracking the Code, geneticist Dr. David Suzuki expressed the belief that “our personal circumstances, our religion, even our sex can change the way our genes affect us. . . . The way genes affect us depends upon our circumstances.” Consequently, he warns: “If you read in the newspapers that scientists have discovered a gene for alcoholism, or criminality, or intelligence, or whatever, take it with a pinch of salt. To tell how a particular gene affects someone, the scientists would need to know everything about that person’s environment as well, and even that might not be enough.”
Indeed not, for yet another factor can influence what you are. The following article considers what this is and how it can affect you for your good.
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• Your body is made of some 100 trillion cells, most of which contain the complete blueprint of you. (Your red blood cells, however, have no nucleus and therefore do not contain the blueprint.)
• Your cells are complex structures, rather like cities with industries, energy-storage depots, and definite routes leading in and out. Direction comes from the cell’s nucleus.
• Your cell’s nucleus, home of your blueprint, can be compared to city hall, where the local government authority generally keeps plans of buildings constructed in the area. To build them, someone has to order materials, line up tools and equipment for the job, and organize the builders.
• Your chromosomes spell out your blueprint. These 23 pairs of tightly spiraling DNA molecules are present in each cell. If all chromosomes in all your body cells were unraveled and joined together, they would stretch to the moon and back some 8,000 times!
• Your DNA has sides joined by pairs of chemical components called bases, like the rungs of a ladder but a ladder twisted into a spiral. The base adenine (A) always joins with thymine (T), cytosine (C) with guanine (G). Split the ladderlike DNA as you would open a zipper, and you reveal the genetic code spelled out in those four letters, A, C, G, and T.
• Your ribosomes, like mobile factories, attach themselves to read the RNA’s (ribonucleic acid) coded message. As they do so, they string together different compounds called amino acids, which form the proteins that make you “you.”
• Your genes are sections of DNA that provide templates by which to make the body’s building blocks, proteins. These genes determine your susceptibility to some diseases. To read your genes, chemical tools called enzymes unzip a stretch of DNA. Other enzymes then “read” their way along the gene, constructing as it goes a complementary series of bases at the rate of 25 a second.
[Box/Picture on page 8]
Extract some of the DNA from human tissues and break it into fragments. Insert the fragments into a gel, pass an electric current through, and then soak the resulting blots onto a thin film of nylon. Add a radioactive gene probe, and photograph. The result is a DNA fingerprint.
Your Future—What Can It Be?
STUDY of the human genome already reveals much about the potential diseases a person may eventually suffer. But what about possible treatment and even the prevention of such illnesses?
The more researchers learn about the genomes of plants, animals, and humans, the greater the possibilities of developing drugs and therapies to treat diseases, asserts The Times of London. Nevertheless, as the magazine Industry Week reports, scientists offer a word of caution because this process “could lag 20 to 50 years behind the diagnosis.” This situation, according to biochemistry professor Charles Cantor, leaves a person “virtually . . . robbed of hope.” But that need not be.
The Bible clearly promises an end to all disease. “[God] will wipe out every tear from their eyes, and death will be no more, neither will mourning nor outcry nor pain be anymore,” states Revelation 21:4. Will geneticists make this come true by what The Christian Century magazine calls “genetic co-creation”? The fulfillment of the Bible’s promises does not depend on the completion of the Human Genome Project, any “genetic co-creation,” or, indeed, a gradual improvement of our environment. Rather, its certainty relies exclusively on God’s active force, his holy spirit.
Counteracting Heredity and Environment
Some three thousand years ago, an Israelite king said: “In a fear-inspiring way I am wonderfully made.” Although David knew nothing of today’s Human Genome Project, he sang this in praise of God: “Your eyes saw even the embryo of me, and in your book all its parts were down in writing.”—Psalm 139:14, 16.
How did this ancient king know that his growth as an embryo in his mother’s womb followed “written” instructions? David himself admitted: “The spirit of Jehovah it was that spoke by me, and his word was upon my tongue.” (2 Samuel 23:2) Yes, the Creator’s active force, holy spirit, inspired David’s writing.
Is there not here a lesson that many people today ignore or, at least, delay to consider? Although heredity and environment to a certain degree make us what we are, God’s holy spirit can powerfully affect us, even counteracting other influences.
Consider the case of Ian. “I was a very excitable little boy,” he explains. “My dad is extremely excitable at times, and now my own little boys are exactly the same. When I was younger, I was terribly nervous. I could not say anything without stuttering and stammering, and then I began using drink as the answer. It calmed me down, or so I thought. Really, drinking made my nerves worse.” When Ian started studying the Bible with Jehovah’s Witnesses, he realized he had to stop relying on alcohol to control his nerves. “I felt that my own willpower was sufficient, and indeed I stopped drinking for a whole year. But,” he admits, “I could not stay stopped.”
“One day,” he continues, “I was walking along the street in the pouring rain thinking that I’d walk until I dropped dead. I had been off drink and back on several times. Then I realized that I had been trying to conquer my drinking problem in my way, not in Jehovah’s way. So I began praying as I walked along, saying to Jehovah, in effect, that I was now going to do things his way, asking him to grant me his holy spirit to strengthen me.” That was some ten years ago. How is Ian now?
“I still have to work to control my weakness,” he admits, “and I have learned to rely heavily on Jehovah to keep going.” To what does Ian attribute his success so far? “I remember my first Bible reading assignment after returning to the congregation of Jehovah’s Witnesses. It was Psalm 116 verse 1, which begins: ‘I do love, because Jehovah hears my voice, my entreaties.’ Halfway through the psalm, I read: ‘What shall I repay to Jehovah for all his benefits to me?’ [Ps 116 verse 12] This was like a stepping-stone that helped me get back to some sort of normality.” Ian now advises any in a similar situation: “Do not deceive yourself.” He adds: “When I finally worked on my problems and prayed for Jehovah’s holy spirit to strengthen my resolve, I began to succeed.”
Ian, along with nearly five million other Witnesses of Jehovah, relies on holy spirit to help him follow the path outlined in the most important instruction book, the Bible. Let the Witnesses in your locality acquaint you with its clear, uncomplicated, simple message—that of God’s Kingdom, his heavenly government in the hands of the resurrected Christ Jesus. This agency will soon remove every trace of genetic flaws and will furnish mankind with a paradise environment in which to live forever. You can be there too!