How does heredity influence personality?

Determining the amount of genetic influence that contributes to the makeup of personality has proved to be a difficult task. However, in studying both fraternal and identical twins, we're able to gain some insight into this mystery. After a series of tests, studies have shown that identical adult twins were more likely to answer questions in the same way than fraternal twins were. In subsequent studies, identical twins who were separated for long periods of time compared to those who weren't separated continued to exhibit the same level of personality traits.