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DNA (From Mrs PORGHO, Lycée of Kongoussi)

In 1953 James Watson and Francis Crick announced the most important scientific discovery of the second half of the 20th century. They had discovered the structure of DNA: the molecule of inheritance, the chemical messenger which carries the genetic information parents pass on to their children. As Watson and Crick found, it has the structure of a double helix.

Society today is only just beginning to understand the consequences of that discovery, made in a dingy laboratory in Cambridge 41 years ago.
One consequence concerns the detection of crime. DNA evidence works by comparing samples of human tissue found at the scenes of crimes -hair, semen and blood, for example-with tissue samples taken from suspects. Convictions have been made after prosecutors told juries that there was only a one –in-a thousand or even a one-in-several-million chance that the DNA evidence "proving" the defendant guilty could be the result of a simple coincidence.

However, there are some doubts about the reliability of the figures. "Expert" scientific witnesses have sometimes disagreed about precisely how probable it is that the match between the suspect’s tissue and that found d at the scene of the crime is due to chance. In one case, the prosecution initially said that the probability of a chance match between the defendant’s DNA sample and blood at the scene of the crime was about 350 million to one. This was later rounded down to 10 million to one. Some scientists have argued that these sorts of figures are arbitrary and not properly calculated.

In spite of doubts about the exact likelihood of a mistaken match, governments are beginning to compile genetic databases on their citizens. In some countries laws require a DNA sample to be extracted from every person convicted of a serious offence. It remains to be seen whether such measures will reduce crime or simply make it easier to catch criminals.


Choose the correct answer to each question from the four choices offered. Justify your answers by indicating the line (s)

1. What aspect of the DNA molecule did the two scientists discover?
a- The way it is constructed
b- its size
c- its role in solving crimes
d- its general usefulness

2. The second paragraph of the text makes the point that society is using information about DNA
a- carelessly
b- with admirable speed
c- in a haphazard way
d- surprisingly late

3. The discovery of the structure of DNA was the most important scientific discovery made
a- between 1900 and 2099
b- between 1900 and 2000
c- between 1900 and 1950
d- between 1951 and 2000

4. DNA enables children
a- to be like their parents
b- to be different from their parents
c- to avoid crime
d- to escape punishment

5- Which of the following could not be used for DNA testing?
a- the suspect’s skin
b- the suspect’s hair
c- the suspect’s pen
d- the suspect’s blood

6- DNA evidence is expressed as
a- proof
b- chance coincidence
c- a degree of probability
d- absolute certainty

7- By placing expert in quotation marks, the writer
a- emphasises the expertise of the scientific witnesses
b- casts doubt on their expertise
c- proves that they are not expert
d- shows his concern at their disagreement

8- That in "and that found at the scene of the crime" (§4) refers to
a- human tissue
b- the match
c- the witness
d- the prosecutor

9- Governments’ actions show that they believe that DNA evidence
a- will lead to an increase in crime
b- should not be allowed to fall into private hands
d- will be useful to them in the future
c- is too unreliable to be trusted

10- The text describes the application of knowledge about DNA in
a- one area of life
b- two areas of life
c- several areas of life
d- all areas of life

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