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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.

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,B,A,C,D