Is Psychiatry Heriditary?

Once a couple asked  a health researcher that they are going to adopt a child whose parental mother had a mild mental illness, they asked whether they would proceed or not, expecting a bright future of the child.
                                  The researcher answered "Generally the mental disorders are seen in later part of the age. The probability of a child to be mental in future being born to a mentally sick parent is very less"
                                According to researchers rather the future mental behaviors of the child depends on the surroundings or the environment in which he or she grows. Heredity plays a minimal role. The diathesis stress-model suggests that heredity alone is not responsible for present or future mental disorder
                                                                                               There is no certainty in anything, sometimes children born to a psychic parent remain healthy throughout  their life. We have to only take care and keep the child in a healthy conducive atmosphere. Even one of the three children of a healthy parent may be psychologically sick