Studies of identical twins, separated to different homes at birth, show low, at most, 40%-50% inheritance or penetrance of even autosomal dominant disease or trait. This means that even if children get a dominant gene, only half will express the disease.
Environmental exposures, diet and stress, all affect genes causing disease. Processes that turn genes on and off in response to the environment (both internal and external), called epigenetic modifications, shift gene expression. Sometimes a gene never gets turned on at all if conditions don’t engage it!
“Your tendency for behaviors is inherited”
Interestingly, neurologic tics, expressed mannerisms, facial grimaces, and stress-related itching patterns are all inherited. Just as interesting, your personal cognitive interests are get passed down through brain hard-wiring. Think of families that share a love for music, of racing cars, or making novel discoveries in a chemistry lab. These mannerisms and intellect show up when external influences such as diet or education resonate with them!