Interesting question, Ghost of Gumby...and while we're not likely to come to a definitive answer, I believe it is less about genetics and more about what we came here with and plan to do here from a soul-level standpoint...genetics provide the physical structure and commonality with whom we are born rather than the personality we come with and further develop while incarnate (my children share our gene pool, but their personalities are lightyears apart). Mama's comment also bears weight from the standpoint her parents, as soulmates, assisted her in developing some particular and valuable traits which have enabled her to play her role in this lifetime, and most likely, in accordance with the lifeplan they each had a hand in planning.
To me, personality is affected by the time and place we are born...the astrological characteristics provide a framework for basic proclivities and default traits. While not locked into those traits, they usually fairly accurately predict one's predilections...and your time, date and location of birth was planned by you with the others in your soulgroup.
Then, while you have access to the characteristics and traits developed through past incarnations, you provided yourself certain primary characteristics and personality strengths which will enable you to have a successful sojourn on earth and to fulfill the plan/script/role you were born to play.
With the framework set up, we are further formed by our environment and those in it who have an impact on how we view the space we occupy...as above, usually those with whom we've planned circumstances which enable our formation into the person we are and are becoming, and ideally we become perfectly outfitted to achieve the purposes for which we came.
