Учебник по НТП

in some organisms may provide the organism with immunity against the disease or an ability to go long periods of time without food.

With this in mind, humans have gene banks to preserve the genetic information in the case of extinction, and nurture species that are at dangerously low population levels. Ironically, the human interference that has disrupted so many species can now provide a means of placing genes into organisms, therefore preparing them for the above hypothetical scenarios such as an epidemic of disease. Genetic engineering would provide the means of allowing organisms to suit their environment without the trial and error over time that comes from natural selection.

In general, the owners of the domesticated animals use three strategies to refine local populations:

1. Isolation. There must be a period in which the members of the group are relatively fixed, so that no new genetic material comes in. Without genetic isolation of the group, the differentiation that creates a new breed cannot take place.

2.Artificial selection. Breeders must prevent random mating from coming about, and limit mating to those individuals who exhibit desired characteristics. One logical consequence of this isolation is the next characteristic: inbreeding.

3.Inbreeding. Ordinarily those who are controlling the artificial breeding will find it necessary at some stage to employ a degree of linebreeding (mating within one bloodline, or strain) or inbreeding (mating closely related individuals), to facilitate the weeding-out of undesired characteristics and the fixation of desired traits. Inbreeding and linebreeding are controversial aspects of artificial selection, but have been practiced for centuries.

A studbook is the official registry of approved individuals of a given breed kept by a breed association. It is said to be “closed” if individuals can be added only if their parents were both registered. It is said to be “open” if individuals can be added without their parents being registered, such as by inspection. Studbooks have been kept for centuries; the concept of the breed associations and clubs is more recent. Most of the “purebred horses” have open studbooks while the studbooks of purebred dogs only remain open if the breed is under development or if there is deemed to be an insufficient gene pool. In some registries, breeders may apply for permission to crossbreed other breeds into the line to emphasize certain traits, to keep the breed from extinction or to alleviate problems caused in the breed by inbreeding from a limited set of animals. A related preservation method is backbreeding, used by some equine and canine registries, in which crossbred individuals are mated back to purebreds to eliminate undesirable traits acquired through the crossbreeding.

The very idea of ‘breed purity’ often strikes an unpleasant chord with

133

modern animal fanciers because it is reminiscent of nineteenth-century eugenics notions of the “superior strain” which were supposedly exemplified by human aristocracies and thoroughbred horses. The application of theories of eugenics has had far-reaching consequences for human beings, and the observable phenomenon of hybrid vigor stands in sharp contrast.

The Appaloosa horse, which was developed by the Nez Perce Indians in the Northwest United States, provides an example. The Spanish colonists had established horse breeding in what is now New Mexico by about 1600, and the Spaniards of that era were known to have horses with spotted coats. By 1806 the Nez Perce were observed to have developed strong, hardy, spotted horses. It is not known if the Nez Perce practiced inbreeding, but they were reputed to geld stallions judged unsuitable for breeding, and to trade away mares likewise unsuitable for breeding, which accomplishes the goals of isolation and artificial selection.

a of the superior strain was that by “breeding the best to the best,” employing sustained inbreeding and selection for “superior” qualities, one would develop a bloodline superior in every way to the unrefined, base stock which was the best that nature could produce. Naturally the purified line must then be preserved from dilution and debasement by base-born stock. This theory was never completely borne out. It can be said that when the ideal of the purified lineage or aesthetic type is seen as an end in itself, the breed suffers over time. The same issues are raised in the world of purebred cats. His claim that selective breeding had been successful in producing change over time was one of the key arguments proposed by Charles Darwin to support his theory of natural

selection in his acclaimed yet controversial work Origin of Species.

134

VIII. Mastering English Grammar

Translate the sentences paying special attention to the equivalent-lacking grammatical structures:

1. The term «genetics» did not even appear until 1909, only 2 years before Galton’s death. With or without a formal name, the study of heredity always has been, at its core, the study of biological variation.

2.With or without a formal name, the study of heredity always has been, at its core, the study of biological variation.

3.We and they share behaviors that are characteristic of highly social primates, including nurturing, cooperation, altruism, and even some facial expressions.

4.Conserved behaviors are part of that history, which is written in the language of nature’s universal information molecule—DNA.

5.In particular, the statistical argument relies on the natural process of «crossing over,» in which the matching chromosomes of each parent pair up and sometimes exchange pieces of DNA.

6.When scientists begin searching for a gene that may be related to a complex human characteristic, they usually know nothing about the likely location of the gene, the protein that it specifies, or the function of that protein.

7.If a marker is consistently found in individuals who have a particular characteristic, and not found in other individuals, then it is inferred that there is a gene near the marker which is «linked» to the characteristic.

8.In some cases, investigators begin with an educated guess: rather than using random genetic markers, they look for linkage to particular genes that have already been identified, called candidate genes, which they believe might function in the behavior under study.

9.Huntington’s disease, for example, is a complex behavioral disorder which is known to be caused by a single gene.

10.No single gene determines a particular behavior. Behaviors are complex traits involving multiple genes that are affected by a variety of other factors.

Identical twins, formed when one fertilized egg splits, are the only people in the world with identical DNA, though it is expressed in different ways (phenotypes). Traits determined by phenotype, such as fingerprints and physical appearance, are the result of the interaction of the individual’s genes and the developmental environment in the uterus. Thus, a DNA test can’t determine the difference between identical twins, while a simple fingerprint can.

135

IX. Fostering Critical Thinking Skills

Read the text. Find additional material to expand the topic and write a commented essay in Russian on Genes and Genetics

Nature or Nurture?

It has long been observed that certain human behavioral characteristics tend to «run in families». These characteristics might be caused by either genes or environments, or some combinations of the two. Sir Francis Galton (1822-1911) was the first scientist to study heredity and human behavior systematically. The term «genetics» did not even appear until 1909, only 2 years before Galton’s death. With or without a formal name, the study of heredity always has been, at its core, the study of biological variation. Human behavioral genetics, a relatively new field, seeks to understand both the genetic and environmental contributions

to individual variations in human behavior.

Behavior has an evolutionary history that persists across related species. Chimpanzees are our closest relatives, separated from us by a mere 2 percent difference in DNA sequence. We and they share behaviors that are characteristic of highly social primates, including nurturing, cooperation, altruism, and even some facial expressions. Genes are evolutionary glue, binding all of life in a single history that dates back some 3.5 billion years. Conserved behaviors are part of that history, which is written in the language of nature’s universal information molecule—DNA.

Experiments linking a gene to a complex human characteristic generally rely on a statistical argument that a segment of DNA and a complex characteristic tend to co-occur in individuals more often than one would expect at random. In particular, the statistical argument relies on the natural process of «crossing over,» in which the matching chromosomes of each parent pair up and sometimes exchange pieces of DNA. Thus, two genes that had begun on the same chromosome can end up on different chromosomes. The probability that two stretches of DNA will end up in the same gamete (and thus the same person), despite crossing over, is related to their proximity on the chromosome: the closer together they are, the more likely they are to remain on the same chromosome.

When scientists begin searching for a gene that may be related to a complex human characteristic, they usually know nothing about the likely location of the gene, the protein that it specifies, or the function of that protein. Instead of directly examining whether a particular gene causes a particular characteristic, they use easily traceable pieces of DNA, called genetic markers, to narrow down the possible location of such a gene.

136

If a marker is consistently found in individuals who have a particular characteristic, and not found in other individuals, then it is inferred that there is a gene near the marker which is «linked» to the characteristic. The gene need not include the marker; if they are sufficiently close together, they will tend to remain together despite crossing over. Thus, linkage between a marker and a trait does not indicate that a relevant gene has been identified, but may indicate that a relevant locale has been found.

In some cases, investigators begin with an educated guess: rather than using random genetic markers, they look for linkage to particular genes that have already been identified, called candidate genes, which they believe might function in the behavior under study. Experiments on non-human animals sometimes suggest candidate genes, but this by no means guarantees that a similar gene in human beings will be linked to the behavior of interest.

This type of research has been very successful in locating genes that cause a disease in an all-or-none manner. Huntington’s disease, for example, is a complex behavioral disorder which is known to be caused by a single gene. But the inheritance pattern for Huntington›s disease is very different from inheritance patterns for conditions like manicdepression, schizophrenia, and alcoholism.

No single gene determines a particular behavior. Behaviors are complex traits involving multiple genes that are affected by a variety of other factors. With disorders, behaviors, or any physical trait, genes are just a part of the story, because varieties of genetic and environmental factors are involved in the development of any trait. Having a genetic variant doesn›t necessarily mean that a particular trait will develop. The presence of certain genetic factors can enhance or repress other genetic factors. Genes are turned on and off, and other factors may be keeping a gene from being turned «on.» In addition, the protein encoded by a gene can be modified in ways that can affect its ability to carry out its normal cellular function. Genetic factors also can influence the role of certain environmental factors in the development of a particular trait. For example, a person may have a genetic variant that is know to increase his or her risk for developing emphysema from smoking, an environmental factor. If that person never smokes, then emphysema will not develop.

Traditional research strategies in behavioral genetics include studies of twins and adoptees, techniques designed to sort biological from environmental influences. More recently, investigators have added the search for pieces of DNA associated with particular behaviors, an approach that has been most productive to date in identifying potential locations for genes associated with major mental illnesses such as schizophrenia and bipolar disorder. Genetics and molecular biology

137

have provided some significant insights into behaviors associated with inherited disorders. For example, we know that an extra chromosome 21 is associated with the mental retardation that accompanies Down›s syndrome, although the processes that disrupt brain function are not yet clear. We also know the steps from gene to effect for a number of single-gene disorders that result in mental retardation, including phenylketonuria (PKU), a treatable metabolic disorder for which all newborns in the United States are tested.

Twin and adoption analyses provide strong evidence that genes influence individual differences in temperament, continuity and change in temperament and, at least in part, mediate the link between temperament and behavior problems. However, the genetic effects in these analyses are anonymous. That is, quantitative genetic designs indicate the magnitude of genetic influence, but do not identify specific genes responsible for heritability. One of the most exciting new directions for research on personality and temperament comes from recent advances in molecular genetic techniques that now make it possible to identify genes associated with complex phenotypes.

In general, it is easier to discern the relationship between biology and behavior for chromosomal and single-gene disorders than for common, complex behaviors that are of considerable interest to specialist and nonspecialist alike. So the former are at the more informative end of a sliding scale of certainty with respect to our understanding of human behavior. At the other end of the scale are the hard-to-define personality traits, while somewhere in between are traits such as schizophrenia and bipolar disorder—organic diseases whose biological roots are undeniable yet unknown and whose unpredictable onset teaches us about the importance of environmental contributions, even as it reminds us of our ignorance.

138

Are behaviors inbred, written indelibly in our genes as immutable biological imperatives, or is the environment more important in shaping our thoughts and actions? What social consequences would genetic diagnoses of such traits as intelligence, criminality, or homosexuality have on society? What effect would the discovery of a behavioral trait associated with increased criminal activity have on our legal system?

Such questions cycle through society repeatedly, forming the public nexus of the «nature vs. nurture controversy,» a strange locution to biologists, who recognize that behaviors exist only in the context of environmental influence. Nonetheless, the debate flares anew every few years, reigniting in response to genetic analyses of traits such as intelligence, criminality, or homosexuality, characteristics freighted with social, political, and legal meaning.

X. Organizing Ideas

Make a concept map on Genetics and fill it with basic notions and associated words and phrases you’ve learned in this unit.

139

Unit III

Illnesses And Treatment

I. Getting Started

Read the text “Computed Tomography Scan“. Divide it into several key parts and compose 3-5 questions to the each part. Put your questions to class.

II. Working With Vocabulary

Place the words and phrases below into the “Word“ column and complete the table:

	Word	English	Example	Russian
		definition	of usage	translation

computed tomography, fraction of a second, dense tissues, dough- nut-shaped scanner, intravenous, oral contrast material, intrathecally, to metastasize, enlarged lymph node, foreign object, inflammatory disease, deformity, blockage, ultrasound test, to develop an allergic reaction, to control a reaction, hay fever, water loss, kidney failure, to have a history of problems, radiologist, helical and multislice CT scanners, electron beam CT scanning, accurate picture, CT angiography, twoand three-dimensional images.

III. Practising Translation Techniques

Make a written translation of the following text:

Computed Tomography Scan

Acomputed tomography (CT) scan uses X-rays to produce detailed pictures of structures inside the body. A CT scan is also called a computerized axial tomography (CAT) scan. A computed tomography scanner directs a series of X-ray pulses through the body. Each X-ray pulse lasts only a fraction of a second and represents a “slice” of the organ or area being studied. The slices or pictures are recorded on a computer and can be saved for further study or printed out as photographs. Dense tissues, such as bones, appear white in the pictures produced by a CT scan, less dense tissues, such as brain tissue or

140

muscles, appear in shades of gray, and air-filled spaces, such as in the bowel or lungs, appear black.

CT scanning can be used to obtain information about almost any body organ (such as the liver, pancreas, intestines, kidneys, adrenal glands, lungs, and heart), blood vessels, the abdominal cavity, bones, and the spinal cord. During a CT scan, the area being studied is positioned inside a doughnut-shaped CT scanner. The scanner can tilt and the X-ray device within it can rotate to obtain the views needed. A dye that contains iodine (contrast material) is often used during a CT scan to make blood vessels and other structures or organs more visible on the CT scan pictures. Intravenous contrast material injected into the blood is used to obtain images of the chest and pelvis; an oral contrast material is given for an abdominal CT scan. Contrast material may be injected into the area around the spinal cord (intrathecally) for spinal scans.

CT scans are used to study many areas of the body, including:

Chest (thorax). A CT scan of the chest can detect infection, lung cancer, pulmonary embolism, and aneurysms. It can also be used to help determine whether cancer has spread (metastasized) into the chest from another location in the body.

Abdomen. A CT scan of the abdomen can help detect several conditions, including cysts, abscesses, infection, tumors, an aneurysm, enlarged lymph nodes, foreign objects, bleeding into the abdominal cavity, inflammatory bowel disease, and appendicitis.

Liver. A CT scan can detect liver tumors, bleeding from the liver, the cause of jaundice, and some liver diseases.

Pancreas. A CT scan can detect a tumor in the pancreas or inflammation of the pancreas (pancreatitis).

141

Gallbladder, bile ducts and spleen. A CT scan can be used to investigate blockage of the bile ducts or to evaluate injury to the spleen. Gallstones occasionally show up on a CT scan, but an ultrasound test is usually used to detect gallstones.

Spine and spinal bones (vertebrae). A CT scan can detect tumors, injuries, deformities, narrowing of the spinal canal (spinal stenosis), and other problems of the spine. The test can also identify a herniated disc of the spine and help determine whether complications of osteoporosis are present.

The risks of a CT scan causing a problem are small. There is a slight risk of developing an allergic reaction to the iodine contrast material. The reaction can be mild (itching, rash) or severe (difficulty breathing or sudden shock). Death resulting from an allergic reaction is rare. Most reactions can be controlled using medication. Be sure to tell your health professional if you have allergies of any kind, such as hay fever, iodine allergy, eczema, hives, or food allergies.

The contrast material used during CT scanning can cause water loss or damage to the kidneys that may lead to kidney failure. This is a concern if you are dehydrated or have poor kidney function. If you have a history of kidney problems, blood tests (creatinine, blood urea nitrogen) may be done before the CT scan to check that your kidneys are functioning properly. If contrast material is used, you may be at risk for kidney problems if you have diabetes, especially if you take metformin (Glucophage). You will need to stop taking metformin for a period of time before the test and resume taking it as directed by your doctor or the radiologist. There is always a slight risk of damage from being exposed to any radiation, including the low levels of X-rays used for a CT scan. However, the risk of damage from the X-rays is usually very low compared with the potential benefits of the test.

CT scans are widely used in our days. Special CT scanners called spiral (helical) CT scanners and multislice CT scanners can quickly provide a continuous scan of large areas in less than half the time of a standard CT scan. They often are used to diagnose kidney stones, pulmonary embolism, or atherosclerosis.

Electron beam CT scanning is another type of CT scan that can detect atherosclerosis and coronary artery disease. Like a spiral CT, electron beam CT scanning is much faster than a standard CT scan (it can produce an image in a fraction of a second) and can take an accurate picture of an artery even while the heart is beating. CT angiography is a more precise method of evaluating blood vessels than a standard CT scan. CT angiography requires a spiral CT scanner or multislice scanner and uses a combination of dynamic CT scanning and special computer techniques to produce twoand three-dimen- sional images of blood vessels.

142