第二篇DNA Fingerprinting
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 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 based on DNA evidence in the United States occurred 医.学.全.在.线www.lindalemus.comin 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.
36. If two sisters are identical twins, their complete DNAs are
A. the same.
B. unique.
C. different.
D. similar.
37. DNA fingerprinting is a technique of
A. grouping DNA strands into structures.
B. segmenting DNA with probes
C. constructing body tissues by enzymes.
D. identifying a person by comparing DNAs
38. DNA fingerprinting was first used in
A. criminal investigation.
B. animal reproduction.
C. private laboratories
D. genetic disease detection.
39. People question the reliability of DNA fingerprinting for
A. the subjective interpretation of test results.
B. its complex procedure
C. its large scale research.
D. its uniform testing standards.
40. it can be inferred from Paragraph 5 that DNA fingerprinting
A. is costly to the police.
B. could be a social issue.
C. is the only way to prove innocence.
D. has been a profitable business.
第三篇On the Trail of the Honey Badgers
On a recent field trip to the Kalahari Desert, a team of researchers learnt a lot more about honey badgers (獾). The team employed a local wildlife expert, Kitso Khama, to help them locate and follow the badgers across the desert. Their main aim was to study the badgers’ movements and behaviour as discreetly (谨慎地) as possible, without frightening them away or causing them to change their natural behaviour. They also planned to trap a few and study them close up before releasing them. In view of the animal’s医.学.全.在.线www.lindalemus.com reputation, this was something that even Khama was reluctant to do.
“The problem with honey badgers is they are naturally curious animals, especially when they see something new,” he says. “that, combined with their unpredictable nature, can be a dangerous mixture. If they sense you have food, for example, they won’t be shy about coming right up to you for something to eat. They’re actually quite sociable creatures around humans, but as soon as they feel they might be in danger, they can become extremely vicious (凶恶的). Fortunately this is rare, but it does happen.”
The research confirmed many things that were already known. As expected, honey badgers ate any creatures they could catch and kill. Even poisonous snakes, feared and avoided by most other animals, were not safe from them. The researchers were surprised, however, by the animal’s fondness for local melons, probably because of their high water content. Previously researchers thought that the animal got all of its liquid requirements from its prey (猎物). The team also learnt that, contrary to previous research findings, the badgers occasionally formed loose family groups. They were also able to confirm certain results from previous research, including the fat that female badgers never socialized with each other.
Following some of the male badgers was a challenge, since they can cover large distances in a short space of time. Some hunting territories cover more than 500 square kilometers. Although they seem happy to share these territories with other males, there are occasional fights over an important food source, and male badgers can be as aggressive towards each other as they are towards other species.
As the badgers became accustomed to the presence of people, it gave the team the chance to get up close to them without being the subject of the animal’s curiosity — or their sudden aggression. The badgers’ eating patterns, which had been disrupted, returned to normal. It also allowed the team to observe more closely some of the other creatures that form working associations with the honey badger, as these seems to adopt the badgers’ relaxed attitude when near humans.
41. Why did the wildlife experts visit the Kalahari Desert?
A. To find where honey badgers live.
B. To observe how honey badgers behave.
C. To catch some honey badgers for food.
D. To find out why honey badgers have a bad reputation.
42. What does Kitso Khama say about honey badgers?
A. They show interest in things they are not familiar with.
B. They are always looking for food.
C. They do not enjoy human company.
D. It is common for them to attack people.
43. What did the team find out about honey badgers?
A. There were some creatures they did not eat.
B. They may get some of the water they needed from fruit.
C. They were afraid of poisonous creatures.
D. Female badgers did not mix with male badgers.
44. Which of the following is a typical feature of male badgers?
A. They don’t run very quickly.
B. They hunt over a very large area.
C. They defend their territory from other badgers.
D. They are more aggressive than females
45. What happened when honey badgers got used to humans around them?
A. They became less aggressive towards other creatures.
B. They lost interest in people.
C. They started eating more.
D. Other animals started working with them.
