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

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

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