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About the Research Using Twins Reading Passage
This passage examines why twins — both identical (monozygotic) and non-identical (dizygotic) — are uniquely valuable to scientific research. It explores how researchers use twin studies to separate the effects of genetic inheritance from environmental influences on traits ranging from language development to disease susceptibility. The passage is sourced from Cambridge IELTS 9, Academic Test 4, Passage 1.
You should spend about 20 minutes on Questions 1–13, which are based on the passage below.
The passage contains two question types: True/False/Not Given (Questions 1–7) and Summary Completion (Questions 8–13).
Research Using Twins — Full Reading Passage
Paragraph A
To biomedical researchers all over the world, twins offer a precious opportunity to untangle the influences of genes and the environment. Because identical twins result from the splitting of a single fertilised egg, they share virtually 100 per cent of their genes. Non-identical twins, however, develop from two separate eggs and share only around 50 per cent of their genes, just like any other brother or sister. If a characteristic in twins is mainly influenced by genetics, then identical twins should be more alike than non-identical twins in that characteristic. Conversely, if the environment has a stronger influence on a characteristic, identical and non-identical twins should be equally alike or unlike. By studying large numbers of twins, researchers can estimate how much of the variation in a particular characteristic is due to genes and how much is due to the environment.
Paragraph B
Twins come in two distinct types: identical (monozygotic) and non-identical (dizygotic). Identical twins are always the same sex, since they come from a single fertilised egg that has divided into two. In contrast, non-identical twins can be the same sex or different sexes. Despite popular belief, being a twin does not run in families for identical twins. Dizygotic twinning, however, does run in families. For researchers, the most useful type of study is one which compares identical with non-identical twins: differences between the two types can reveal the relative role of biology and environment in shaping human characteristics.
Paragraph C
Using twins to study the development of human characteristics such as behaviour and intelligence is not new. What is new is an awareness of the scope of twin research and the possibilities it opens up, particularly for medical research. The existence of twins who were raised apart is of special interest to researchers. When twins who shared a very similar environment during childhood are found to be different, this strengthens the belief that the variation between them has a genetic cause. Conversely, where twins raised apart are similar, this suggests the characteristic has been strongly influenced by natural behaviour patterns rather than by the environment.
Paragraph D
Studies of twins can reveal the relative contributions of genetics and environment to a range of conditions, from cancer to mental health. Some of the most striking findings concern conditions previously thought to be mainly environmental in origin. Coronary heart disease, for example, and high blood pressure, appear to have a surprisingly large genetic component. Conditions such as schizophrenia and manic depression have also been shown to have a strong genetic component. Research into the significance of such findings for health is ongoing.
Paragraph E
Twin studies have also shed light on conditions that involve abnormalities of body weight. Although it is widely accepted that people with a tendency to put on weight can, to some degree, blame their genes, few researchers initially expected genetics to play such a dominant role. But early results from large twin studies show that conditions such as obesity, anorexia nervosa and bulimia nervosa are all substantially heritable. In other words, genes account for the majority of variation between individuals in these conditions. It does not mean, however, that environmental factors play no part — rather, that their role is smaller than had been assumed.
Paragraph F
Other areas where twin research is producing interesting results include the development of reading abilities and other cognitive traits, as well as the design of new medical treatments. Findings from large-scale twin studies can be used to develop and evaluate the effectiveness of treatments for conditions that have a strong genetic component. Rather than simply treating the symptoms of a disease, researchers can investigate the genetic basis of a condition and develop treatments that target those specific genetic pathways. Twin studies are therefore increasingly important to the future of medical treatment, particularly in the field of genetic medicine.
Paragraph G
Not all twins are enthusiastic about being research subjects, however. Some express concerns about the use of their genetic data, fearing that the information could be shared with insurance companies or employers. Confidentiality is a primary concern. Researchers are careful to preserve the anonymity of participants; nevertheless, the issue of privacy remains a point of debate in the wider discussion about the ethics of genetic research.
Research Using Twins Reading Questions and Answers
Questions 1–7: True/False/Not Given
Do the following statements agree with the information given in the Reading Passage?
Write:
- TRUE — if the statement agrees with the information
- FALSE — if the statement contradicts the information
- NOT GIVEN — if there is no information on this
1. Identical twins have exactly the same genetic makeup.
2. Non-identical twins are more common than identical twins.
3. The fact that a person is a twin is inherited for both types of twins.
4. Research on twins raised apart can be useful in confirming whether genetics or environment is responsible for a particular characteristic.
5. Studies of twins have shown that schizophrenia is caused entirely by genetic factors.
6. Environmental factors are thought to be the main reason why some people develop obesity.
7. Some twins are worried about their personal data being passed on to third parties.
Questions 8–13: Summary Completion
Complete the summary below.
Choose NO MORE THAN ONE WORD from the passage for each answer.
Twin studies are valuable to researchers because they can separate genetic from environmental influences on human characteristics.
The most informative comparisons are between identical and non-identical twins, which can reveal the role of 8 ________ versus the environment. Studies of twins raised apart have been especially useful in exploring natural 9 ________ patterns. More recently, researchers have turned to twin studies to investigate 10 ________ conditions, including heart disease and mental illness. One important discovery is that 11 ________ and related eating disorders are largely genetic in origin. Twin studies are also helping to improve 12 ________ for conditions with a strong genetic component. Some twins, however, are concerned about 13 ________ and the use of their genetic data.
