You are a good person. Is it necessary to be inflicted with a genetic weakness from an ancestor? The soul before entering the physical body does have a general idea of the challenges ahead. Hereditary tendencies are weakened or intensified according to consciousness and lifestyle choices. Two people could have the identical challenges yet; the out come is not identical. Soul history and choice determine how a weakness does or does not manifest. The belief system is the greatest influence.
The worse case example is the scenario where a person repetitively comments on how her mother, aunt, and grandmother all experienced a particular disease. The young mother I knew almost seemed to relish the tale of woe and how she was certain that she, too, would die of cancer. She kept feeding her belief system and it grew into a cancer that eventually killed her and deprived her young son of a mother.
Because there is a possible weakness in the genetic history doesn’t mean you have to claim it as your own. It is a perfect opportunity for us to use the mind in a scientific way and deprogram negative influences and create a higher energy that will challenge and diminish any harmful effects.