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第三篇
DNA fingerprinting
DNA is the genetic material found within the cell nuclei of all living things. In mammals the stands 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 DNA. A DNA 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 base on DNA evidence in the United States occurred in 1998. 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.
练习
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.
C. unique.
D. lost.
标准答案： C,B,A
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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 the results of their tests.
D. suspects may not have enough money to provide their own DNA to law-courts.
5. Their essay talks about DNA fingerprinting concerning the following aspects EXPECT
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.
标准答案： C,D
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第五部分：补全短文(每题2分，共10分)
阅读下面的短文，文章中有5处空白，文章后有6组文字，请根据文章的内容选择5组文字，将其分别放会文章原有位置，以恢复文章原貌。请将答案涂在答题卡相应的位置。
Why do people shrink?
Did you ever see the movie Honey, I shrunk the kids? It's about a wacky dad (who's also a scientist) who accidentally shrinks his kids with his homemade miniaturizing invention. Oops! ____1____.
For older people, shrinking isn't that dramatic or sudden at all. It takes place over years and may add up to only one inch or so off of their adult height (maybe a little more, maybe less), and this kind of shrinking can't be magically reversed, although there are things that can be done to stop it or slow it down. ___2___.
There are a few reasons. As people get older, they generally lose some muscle and fat from their bodies as part of the natural aging process. Gravity (the force that keeps your feet on the ground) take hold, and the bones in the spine, called vertebrae, may break down or degenerate, and start to collapse into one another. ___3___. But perhaps the most common reason why some older people shrink is because of osteoporosis.
Osteoporosis occurs when too much spongy bone tissue (which is found inside of most bones) is broken down and not enough new bone material is made. ___4___. Bones become smaller and weaker and can easily break if someone with osteoporosis is injured. Older people --especially women, who generally have smaller and lighter bones to begin with -- are more likely to develop osteoporosis. As years go by, a person with osteoporosis shrinks a little bit.
Did you know that every day you do a shrinking act? You aren't as tall at the end of the day as you are at the beginning. That's because as the day goes on, water in the disks of the spine gets compressed (squeezed) due to gravity, making you just a tiny bit shorter. Don't worry, though. ___5___.
A. They end up pressing closer together, which makes a person lose a little height and become shorter.
B. Once you get a good night's rest, your body recovers, and the next morning, you're standing tall again.
C. Over time, bone is said to be lost because it's not being replaced.
D. Luckily, there are things that people can do to prevent shrinking.
E. The kids spend the rest of the movie as tiny people who are barely visible while trying to get back to their normal size.
F. But why does shrinking happen at all?
标准答案： E,F,A,C,B
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