HELP! What evidence indicates that many psychological disorders, such as schizophrenia and developmental disorders, are biologically and not environmentally based?

Schizophrenia and developmental disorders are traced genetically, and the gene will be found in the biological parents of the person with either schizophrenia or developmental disorders.

Explanation:

Although Schizophrenia can be triggered by environmental factors, or the 'nurture' of childhood development, a person who is not predisposed genetically to schizophrenia will not get the psychological disorder. The same is to be said about developmental disorders such as Autism and ADHD, it is hereditary.

For citation of evidence, I recommend talking about prenatal development, and how toxic substances can alter the development of a fetus, which is proven to lead to some developmental disorders, such as Fetal Alcohol Syndrome.