SECTION
2
READING
PASSAGE 2
You should spend about 20 minutes on Questions 14-26 which
are based on Reading Passage 2 below.
Twin Study:
Two of a kind
A
THE scientific study of twins
goes back to the late 19th century, when Francis Galton, an early geneticist,
realised that they came in two varieties: identical twins born from one egg and
non-identical twins that had come from two. That insight turned out to be key,
although it was not until 1924 that it was used to formulate what is known as
the twin rule of pathology, and twin studies really got going.
B
The twin rule of pathology states
that any heritable disease will be more concordant (that is, more likely to be
jointly present or absent) in identical twins than in nonidentical twins – and,
in turn, will be more concordant in non-identical twins than in non-siblings.
Early work, for example, showed that the statistical correlation of skinmole
counts between identical twins was 0.4, while non-identical twins had a
correlation of only 0.2. (A score of 1.0 implies perfect correlation, while a
score of zero implies no correlation.) This result suggests that moles are
heritable, but it also implies that there is an environmental component to the
development of moles, otherwise the correlation in identical twins would be
close to 1.0.
C
Twin research has shown that
whether or not someone takes up smoking is determined mainly by environmental
factors, but once he does so, how much he smokes is largely down to his genes.
And while a person’s religion is clearly a cultural attribute, there is a strong
genetic component to religious fundamentalism. Twin studies are also unraveling
the heritability of various aspects of human personality. Traits from
neuroticism and anxiety to thrill – and novelty-seeking all have large genetic
components. Parenting matters, but it does not determine personality in the way
that some had thought.
D
More importantly, perhaps, twin
studies are helping the understanding of diseases such as cancer, asthma,
osteoporosis, arthritis and immune disorders. And twins can be used, within
ethical, for medical experiments. A study that administered vitamin C to one
twin and a placebo to the other found that it had no effect on the common cold.
The lesson from all today’s twin studies is that most human traits are at least
partially influenced by genes. However, for the most part, the age-old
dichotomy between nature and nurture is not very useful. Many genetic programs
are open to input from the environment, and genes are frequently switched on or
off by environmental signals. It is also possible that genes themselves
influence their environment. Some humans have an innate preference for participation
in sports. Others are drawn to novelty. Might people also be drawn to certain
kinds of friends and types of experience? In this way, a person’s genes might
shape the environment they act in as much as the environment shapes the actions
of the genes.
E
In the past, such research has
been controversial. Josef Mengele, a Nazi doctor working at the Auschwitz
extermination camp during the second world war, was fascinated by twins. He
sought them out among arrivals at the camp and preserved them from the
gas-chambers for a series of brutal experiments. After the war, Cyril Burt, a
British psychologist who worked on the heredity of intelligence, tainted twin
research with results that appear, in retrospect, to have been rather too good.
Some of his data on identical twins who had been reared apart were probably
fakes. In any case, the prevailing ideology in the social sciences after the
war was Marxist, and disliked suggestions that differences in human potential
might have underlying genetic causes. Twin studies were thus viewed with
suspicion.
F
The ideological pendulum has
swung back; however, as the human genome project and its aftermath have turned
genes for abstract concepts to real pieces of DNA. The role of genes in
sensitive areas such as intelligence is acknowledged by all but a few
die-hards. The interesting questions now concern how nature and nurture
interact to produce particular bits of biology, rather than which of the two is
more important. Twin studies, which are a good way to ask these questions, are
back in fashion, and many twins are enthusiastic participants in this research.
G
Research at the Twinsburg festival began in a small way,
with a single stand in 1979.
Gradually, news spread, and more
scientists began turning up. This year, half a dozen groups of researchers were
lodged in a specially pitched research tent. In one corner of this tent, Paul
Breslin, who works at the Monell Institute in Philadelphia, watched over
several tables where twins sat sipping clear liquids from cups and making
notes. It was the team’s third year at Twinsburg. Dr Breslin and his colleagues
want to find out how genes influence human perception, particularly the senses
of smell and taste and those (warmth, cold, pain, tingle, itch and so on) that
result from stimulation of the skin. Perception is an example of something that
is probably influenced by both genes and experience. Even before birth, people
are exposed to flavours such as chocolate, garlic, mint and vanilla that pass
intact into the bloodstream, and thus to the fetus. Though it is not yet clear
whether such pre-natal exposure shapes taste-perception, there is evidence that
it shapes preferences for foods encountered later in life.
H
However, there are clearly
genetic influences at work, as well – for example in the ability to taste
quinine. Some people experience this as intensely bitter, even when it is
present at very low levels. Others, whose genetic endowment is different, are
less bothered by it. Twin studies make this extremely clear. Within a pair of
identical twins, either both, or neither, will find quinine hard to swallow.
Non-identical twins will agree less frequently.
I
On the other side of the tent
Dennis Drayna, from the National Institute on Deafness and Other Communication
Disorders, in Maryland, was studying hearing. He wants to know what happens to
sounds after they reach the ear. It is not clear, he says, whether sound is
processed into sensation mostly in the ear or in the brain. Dr Drayna has
already been involved in a twin study which revealed that the perception of
musical pitch is highly heritable. At Twinsburg, he is playing different words,
or parts of words, into the left and right ears of his twinned volunteers. The
composite of the two sounds that an individual reports hearing depends on how
he processes this diverse information and that, Dr Drayna believes, may well be
influenced by genetics.
J
Elsewhere in the marquee, Peter
Miraldi, of Kent State University in Ohio, was trying to find out whether genes
affect an individual’s motivation to communicate with others. A number of twin
studies have shown that personality and sociability are heritable, so he thinks
this is fertile ground. And next to Mr. Miraldi was a team of dermatologists
from Case Western Reserve University in Cleveland. They are looking at the
development of skin disease and male-pattern baldness. The goal of the latter
piece of research is to find the genes responsible for making men’s hair fall
out.
K
The busiest part of the tent, however, was the queue for
forensic-science research into fingerprints. The origins of this study are
shrouded in mystery. For many months, the festival’s organisers have been
convinced that the Secret Service – the American government agency responsible
for, among other things, the safety of the president – is behind it. When The
Economist contacted the Secret Service for more information, we were referred
to Steve Nash, who is chairman of the International Association for
Identification (IAI), and is also
a detective in the scientific investigations section of the Marin Country
Sheriff’s Office in California. The IAI, based in Minnesota, is an organisation
of forensic scientists from around the world. Among other things, it publishes
the Journal of Forensic Identification.
Questions
14-18
The Reading Passage has seven
paragraphs A-K
Which paragraph contains the
following information?
Write the correct letter A-K, in boxes 14-18 on your answer sheet.
NB
You may use any letter more than
once.
14
Mentioned research conducted in Ohio
15
Medical contribution to the researches for
twins.
16
Research situation under life threatening
conditions
17
Data of similarities of identical twins
18
Reasons that make one study unconvincing
Questions
19-20
Complete the
following summary of the paragraphs of Reading Passage 2 Using NO MORE THAN TWO WORDS from the Reading
Passage for each answer.
Write your answers in boxes 19-20 on your answer sheet.
The first one that conducted
research on twins is called 19…………………………
He separated twins into two categories: non identical and identical twins. The
twin research was used in medical application in as early as the year of 20………………………….
Questions
21-23
Choose the correct letters in
following options:
Write your answers in boxes 21-23 on your answer sheet.
Please choose THREE research fields that had been
carried out in Ohio, Maryland and Twinburgh?
A Sense
B Cancer
C Be
allergic to Vitamin D
D Mole
heredity
E
Sound
F
Boldness of men
Questions
24-26
Choose the correct letters in
following options
Write your answers in boxes 24-26 on your answer sheet.
Please choose THREE results that had been verified in this passage.
A Non
identical twins come from different eggs.
B Genetic
relation between identical twins is closer than non-identical ones.
C Vitamin
C has evident effect on a cold.
D Genetic
influence to smoking is superior to environment’s
E
If a pregnant woman eats too much sweet
would lead to skin disease.
F
Hair loss has been found to be connected
with skin problem.
ANSWERS
ANSWER
14. J
15. D
16. E
17. B
18. E
19. Francis Galton
20. 1924
21. A
22. E
23. F
24. A
25. B
26. D
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