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A new study shows that while identical twins can look perfectly alike, it is not a perfect similarity. They are not clones each other. Scientists the University Iceland analyzed the DNA 387 pairs of identical twins - babies born from a single fertilized egg. The scientists compared the DNA with that the twins' parents and children. The geneticists looked mutations in the early stages of development. A mutation is a tiny change the sequence of the DNA that can occur when a cell divides. This change causes a slight difference the DNA replication process. A single, tiny change can create differences height, intelligence, eye colour and even susceptibility to disease.

The study shows that identical twins do not share totally identical DNA. In 15 per cent of identical twin pairs, one twin carried a "substantial" number mutations that the other did not share. The scientists say this difference is important as it sheds light the "nature versus nurture" debate. This is whether human behaviour is determined the environment, socialization and upbringing, or a person's genes. The research shows that this tiny difference, and not environmental factors, could be the reason why one twin develops different behavioural characteristics or medical conditions. Professor Kari Stefansson said a genetic mutation may be the source a given disease or trait.

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