Question

Other than genes, what is the other major factor that helps define our traits?

Answer 1

Another major factor that can change our traits, other then our genes, is the environment.
There is a interaction between our genes and the environment. For example, two identical twins that go through different environments end up with different personalities, even though they share the same DNA.

Answer 2

Besides genes, our phenotypic expression is also influenced by environmental factors. For example, genes will control a base skin color, but exposure to sunlight will darken the skin.