What are the hereditary factors behind exceptionality?

The adage that some unfortunate people begin their life's journey with fewer advantages or greater disadvantages than others, while only a select few fortunate people start their life's journey with greater advantages, clearly illustrates the importance of hereditary contributions in laying the solid foundation stone of the exceptionality visible in the child at birth or onwards. A person's genetic endowments have always been linked to situations of positive exceptionality, such as great mental abilities and creativity, and cases of negative exceptionality, such as familial mental retardation (retardation without evident neurological injury).