第四十五篇 DNA Fingerprinting【DNA指纹】
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．
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 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．
DNA指纹
DNA是所有生物细胞核子发现的基因材料。哺乳动物的DNA线被组合为称作染色体的各种结构。除生物姊妹体外（如完全相同的双胞胎），每一个体的整条DNA是独一无二的。
DNA指纹有时也称作DNA印记法。这是一种通过比较少量DNA的鉴别方法。DNA指纹的构成先要从身体组织或液体中抽取DNA标本，如头发、血液或唾液。采取的标本用酶分割成若干部分，各切片根据大小排列。切片先用探针做标记，然后曝光于X光片上。胶片上形成由黑色条纹组成的图案，这就是DNA指纹。若两个不同标本的DNA指纹完全相像，则这两个标本可能来自同一人。
DNA指纹首次作为鉴别技术进行开发是在1985年。开始是用来探测遗传疾病的，很快便被应用于刑事调查与法律事务。基于DNA所提供证据的首例定罪是1988年，在美国。在刑事调查中，把从犯罪现场采集的证据中提取的DNA村本与犯罪嫌疑人的相比。一般说来，法庭已承认DNA测试的可靠性并允许DNA测试结果纳为证据然而，在一些方面DNA指纹颇具争议性：结果的精确性，测试成本及技术的错误使用的可能性。
由于一些原因，DNA指纹的精确性受到了挑战。首先，由于是DNA切片而并非完整的DNA被作为指纹进行研究；DNA指纹可能并非独一无二的；尚未进行过大规模研究以证实DNA指纹测试结果是独一无二的。此外，DNA指纹常是在私人实验室作的，可能并不遵循统一的测试标准与质量控制。再有，既然必须由人来解释测试，人为的错误可能导致错误结果。
DNA指纹颇为昂贵。如果犯罪嫌疑人不能将自己的DNA提供给专家，他/她就很可能没有确凿的证据证明自己无罪。为鉴定目的而作的DNA测试的广泛使用可能会导致DNA指纹数据库的建立。
完形填空：
第十三篇 Scientists Develop Ways of Detecting Heart Attack
【科学家探索发现心脏病的方法】
German researchers have __ 1 __ a new generation of defibrillators and early－warning software aimed at offering heart patients greater protection __ 2 __ sudden death from cardiac arrest．
In Germany alone around 100，000 people die annually as a result of cardiac arrest and many of these cases __ 3 __ by disruption to the heart’s rhythm． Those most at risk are patients who have __ 4 __ suffered a heart attack， and for years the use of defibrillators has proved useful in diagnosing __ 5 __ disruption to heart rhythms and correcting them automatically by intervening within seconds． These devices __ 6__ a range of functions， such as that of pacemaker．
Heart specialists at Freiburg’s University Clinic have now achieved a breakthrough with an implanted defibrillator __ 7 __ of generating a six－channel electrocardiogram （ECG． within the body． This integrated system allows early diagnosis of __ 8__ blood－flow problems and a pending heart attack． It will be implanted in patients for the first time this year． Meanwhile， researchers at the Fraunhofer Institute for Applied Mathematics in Kaiserslautern have developed new computer software that renders of ECG data __ 9 __ ．
The overwhelming __ 10 __ of patients at risk will not have an implanted defibrillator and must for this reason undergo regular ECGs．“Many of the current programs only __ 11__ into account a linear correlation of the data． We are， however， making use __ 12__ a non－linear process that reveals the chaotic patterns of heart beats as an open and complex system，” Hagen Knaf says，“__ 13 __ changes in the heart beats over time can be monitored and individual variations in patients taken into account．” An old study of ECG data， based __ 14__ 600 patients who had suffered a subsequent heart attack， enabled the researchers to compare risks and to show __ 15 __ the new software evaluates the data considerably better．
练习：
1．A come up B come up with
C come up to D come up against
2．A to B for
C with D from
3．A are caused B caused
C are to cause D have been causing
4．A easily B readily
C frequently D already
5．A disease－producing B health－improving
C life－threatening D error－correcting
6．A take in B take after
C take on D take from
7．A capable B able
C skillful D skilled
8．A chronic B acute
C recurrent D persistent
9．A precisely B more precisely
C precision D more precise
10．A maximum B minimum
C majority D minority
11．A get B take
C bring D fetch
12．A of B with
C for D in
13．A Similarly B In this manner
C Otherwise D In this way
14．A in B for
C upon D with
15．A what B where
C that D when
科学家探索发现心脏病的方法
德国研究者们发明了新一代的除颤器和旨在为心脏病人提供更多保护，使他们免遭心脏停止导致的突然死亡的早期预报软件。
仅在德国每年就有10万人死于心脏停止。其中大部分是由于心律中断导致的。危险最大的是那些已经犯过一次心脏病的病人。几年来除颤器被证实在控测心律中止和在几秒中内实施自动干涉以调整心律的诊断中是有用的。这种方法起到了很多作用，例如起博器。
弗莱伯大学诊所的心脏病专家已经在内置除颤器方面取得了突破性成就。这种除颤器可以在体内产生六个频道的心电图。这个综合体系使血液流通总是和即将发生的心脏病可被早些诊断出来。今年它将第一次被植入病人体内。同时，凯瑟劳特的弗劳胡佛实用数学学院的研究者开发了一种新计算机软件。这种软件使心电图数据更加准确。
大部分有风险的患者不能用内置除颤器，因此必须接受常规的心电图检查。“目前的许多计划只把数据的线形关系考虑在内。但是我们现在使用的是能够将心脏跳动的混乱模工作为一个直观而又复杂的系统提示出来的非线性处理方法”。海根•纳夫说，“这样心脏跳动频率的变化就会受到控制，而病人个人的特征也会得到考虑。”一个基于600位犯心脏病的患者的以前的心电图数据研究使科学家们能够比较两种风险，结果显示新软件明显能更好地处理心电图数据。
