The grandmother was diagnosed with ovarian cancer at age 40 and daughter was diagnosed with breast cancer at age 37. The mother lived until the age of 80, was never diagnosed with cancer and died of a heart attack. In the case of the mother, the BRCA1 mutation was non-penetrant while in the daughter and grandmother was penetrant. When a genetic condition is thought to ‘skip a generation’, as in this example, the condition has actually shown reduced or incomplete penetrance.
To view this interactive tutorial, you need the latest Flash player.