Is it Environmental or Genetic?
Nature or nurture? It's probably one of the most frequently asked questions, especially when addressing anti-social behaviour, such as alcoholism or aggression, or trying to find out the root causes of debilitating disorders like depression or heart disease.
So why are identical twins used in genetics research and what can their genomes tell us about the causes of a condition under study?
First of all identical twins have identical genes, non-identical (fraternal) twins do not. So therefore any variations between identical twins are due to the environment.
If a researcher is trying to find out whether genetics or the environment play a greater role in a trait, the genes of identical twins, who share 100% of their genes are compared with the genes of fraternal twins who share 50% of their genes. If the frequency of the trait is greater in the identical twins, it suggests that genes are of importance.
According to the International Society for Mental Health Online, it's been shown that if one identical twin suffers from depression, the other sibling has a 76% chance of also being depressed. If they are raised apart they both become depressed about 67% of the time. In these studies of depression it was also shown that if one fraternal twin suffers from depression, the other sibling has 19% chance of being depressed.