DNA is the genetic material found within the cell nuclei of all living things. In mammals the strands of DNA are grouped into structures called chromosomes. With the exception of identical siblings （as in identical twins）, the complete DNA of each individual is unique.
DNA fingerprinting is sometimes called DNA typing. It is a method of identification that compares bits of DN A. A DAN fingerprint is constructed by first drawing out a DNA sample from body tissue or fluid such as hair, blood, or saliva. The sample is then segmented using enzymes, and the segments are arranged by size. The segments are marked with probes and exposed on X-ray film, where they form a pattern of black bars—the DNA fingerprint. If the DNA fingerprints produced from two different samples match, the two samples probably came from the same person.
DNA fingerprinting was first developed as an identification technique in 1985. Originally used to detect the presence of genetic diseases, it soon came to be used in criminal investigations and legal affairs. The first criminal conviction based on DNA evidence in the United States occurred in 1988. In criminal investigations, DNA fingerprints derived from evidence collected at the crime scene are compared to the DNA fingerprints of suspects. Generally, courts have accepted the reliability of DNA testing and admitted DNA test results into evidence. However, DNA fingerprinting is controversial in a number of areas: the accuracy of the results, the cost of testing, and the possible misuse of the technique.
The accuracy of DNA fingerprinting has been challenged for several reasons. First, because DNA segments rather than complete DNA strands are “fingerprinted”; a DNA fingerprint may not be unique; large-scale research to confirm the uniqueness of DNA fingerprinting test results has not been conducted. In addition, DNA fingerprinting is often done in private laboratories that may not follow uniform testing standards and quality controls. Also, since human beings must interpret the test, human error could lead to false results.
DNA fingerprinting is expensive. Suspects who are unable to provide their own DNA to experts may not be able to successfully defend themselves against charges based on DNA evidence.
Widespread use of DNA testing for identification purposes may lead to the establishment of a DNA fingerprint database.
1. According to the essay, we can find chromosomes
A. in a fish. B. in a tree. C. in a sheep. D. in a rock.
2. DNA fingerprinting is more often used for
A. obtaining samples of chromosomes.
B. providing evidence in court investigations.
C. proving the horse to be a mammal.
D. printing books about biology.
3. When your brother looks exactly like you, your complete DNA may be
A. exactly like his.
B. totally different from his
4. Some people believe that using a DNA fingerprint may not be so reliable because
A. the accuracy of DNA fingerprinting has been challenged.
B. no private laboratory follows uniform testing standards or quality controls.
C. mistakes are possible when researchers explain what have come of their tests.
D. suspects may not have enough money to provide their own DNA to law-courts.
5. This essay talks about DNA fingerprinting concerning the following aspects EXCEPT
A. legal application of the method.
B. the way to obtain a DNA sample.
C. work yet to be done about DNA fingerprinting.
D. possible danger in drawing a DNA sample from the human body.
Education of Students with Vision Impairments
This is specially designed education for children who are either partially sighted or blind. Vision impairments are diagnosed by medical doctors who examine the physical structures in the eye and evaluate the child's ability to see shapes of different sizes at various distances. In the United States, approximately 12 out of 1, 000 children receive some form of special education because of visual impairments.
Partially sighted children may use a variety of adaptive aids to see more clearly and to read printed text. These aids include magnifiers, which may be attached to eyeglasses; electronic systems for enlarging print and making it easier to see; and large-print books. Blind children usually are taught to read Braille, a system of raised dots embossed on paper and read by touch. In the past, turning conventional books into pages of Braille was very time-consuming, and the large books required enormous storage areas. However, most Braille texts are now done electronically. Many students read paperless Braille with the aid of machines that mechanically raise the dots in a small panel as the reader progresses through the text. Because Braille cannot be read very rapidly, many blind students prefer to listen to books being read on tapes. Some students also use reading machines equipped with cameras that scan lines of print, which computers then convert to synthesized speech.
Many blind and partially sighted children receive orientation and mobility training as a part of their education. Specialists teach them how to travel independently in their schools and communities, often with and aid, such as a cane.
Most children with vision impairments are educated in schools within their communities. Vision specialists may provide special materials and equipment, help teachers and classmates understand the children's condition, and possibly provide additional instruction. The specialists may also teach partially sighted children how to use their remaining vision more effectively and instruct them in the use of adaptive aids.
Some children with vision impairments attend special schools designed to meet their particular needs. Like boarding schools, these schools often provide residential services as well as educational programs. They also have specially designed facilities, which may not be found in neighborhood schools, for blind children to participate in athletics and other activities.
The education of many children with vision impairments is further complicated by their having other disabilities, such as physical disabilities, developmental impairments, or hearing loss. Education for those children might emphasize the development of language and communication, and personal, social, and vocational skills rather than academic skills.
1. Various adaptive aids are used to
A. cure children of their vision impairments.
B. help children see more clearly and read books and so on.
C. teach children how to turn Braille into synthesized speech.
D. teach children how to use their remaining vision more effectively.
2. Large-print books are those books which
A. are printed with large pages.
B. have large words in them.
C. can be read by using a magnifier.
D. can be read with the aid of machines.
3. Many blind students like to listen to books because
A. these books can talk by themselves.
B. the synthesized speech is very interesting.
C. this can save time.
D. these students are lazy.
4. “Orientation and mobility training” is meant to teach blind and partially sighted children
A. how to understand part of their education.
B. how to use a cane.
C. how to move around without other people's help.
D. how to help other people to travel independently.
5. It may be good for children with vision impairments to live in special schools because these schools
A. can save the trouble of their coming from and going back homes.
B. are built of nice wooden boards and so are clean and comfortable.
C. have educational programs for the blind.
D. offer training in vocational skills rather than academic skills.
Obesity refers to the medical condition characterized by storage of excess body fat. The human body naturally stores fat tissue under the skin and around organs and joints. Fat is critical for good health because it is a source of energy when the body lacks the energy necessary to sustain life processes, and it provides insulation and protection for internal organs. But too much fat in the body is associated with a variety of health problems.
Most physicians use the body mass index （BMI） to determine desirable weights. BMI is calculated as weight divided by height and people with a BMI of 27 or above are considered obese.
Weight-height tables, such as those published by the Metropolitan Life Insurance Company, are also used as general measures of desirable weight ranges. These tables assign a range of weights for a particular height. For example, a man of 1. 8m has a desirable range of 66 to 83 kg, with an average of 75 kg. A woman who is 1. 6m has a desirable range between 53 and 70 kg, with an average of 62 kg.
The BMI and weight-height tables only provide rough estimates of desirable weights and scientists recognize that many other factors besides height affect weight. Weight alone may not be an indicator of fat, as in the case of a body-builder who may have a high BMI because of a high percentage of muscle tissue, which weighs more than fat. Likewise, a person with a sedentary lifestyle may be within a desirable weight range but have excess fat tissue.
Obesity increases the risk of developing disease. According to some estimates, almost 70 percent of heart disease cases are linked to excess body fat, and obese people are more than twice as likely to develop high blood pressure. Obese women are at nearly twice the risk for developing breast cancer, and all obese people have an estimated 42 percent higher chance of developing colon cancer. The risk of medical complications, particularly heart disease, increases when body fat is distributed around the waist, especially in the abdomen. This type of upper body fat distribution is more common in men than in women.
The social and psychological problems experienced by obese people are also formidable. Stereotypes about “fat ”people are often translated into discriminatory practices in education, employment, and social relationships. The consequences of being obese in a world where people had better be “thin” are especially severe for women, whose appearances are often judged against an ideal of exaggerated slimness.
1. What is obesity?
A. Obesity is having fat tissue under the skin.
B. Obesity is having fat tissue around organs.
C. Obesity is being too fat.
D. Obesity is having good health.
2. If we say that “fat is critical for good health,” we mean that
A. fat people should be criticized.
B. fat is very important for people to keep healthy.
C. people should be fat if they want to be healthy.
D. too much fat in the body is associated with health problems.
3. If a woman is 1.6m tall and weighs 49 kg, she
A. is considered within the desirable weight-height range.
B. is definitely unhealthy.
C. should be considered fat.
D. should not be considered unhealthy.
4. A heavy man
A. certainly has a lot of fat in him.
B. usually has a sedentary lifestyle.
C. certainly has a lot muscle in him.
D. may have muscle tissue that weighs more than fat.
5. According to this article, fat people may be
A. looked down upon by others.
B. welcomed by others.
C. considered severely ill.
D. thought of having special problems.