A Biological Predisposition is an increased chance of developing a disease or pattern of behavior based on the genes we inherited from our parents (and our parents’ parents). Genes influence our personality traits, our IQ, our likelihood of getting cancer, and even our chances of becoming an alcoholic.
Being predisposed to a disorder doesn’t mean that we will definitely develop it, only that we are more vulnerable to it based on our genetic makeup. Biological risk factors combine with environmental factors such as stress or diet to trigger a disorder. (Environment and genes can also protect us from developing certain conditions.)
Research studies using twins have shown that many traits and disorders are heritable. For example, in identical twin pairs, if one twin is diagnosed with schizophrenia, there is a 50% chance that the other twin will also be diagnosed. But in fraternal twin pairs, this rate is only 15%. Because identical twins share more genes than fraternal twins, we can conclude that schizophrenia has an inherited biological basis.