My facination with quantitative genetics can be explained with a simple example. We know that particular variants within the Brca1 gene most certainly increase one’s chances of developing breast cancer and/or ovarian caner. To a statistical geneticist, these variants have a “large effect”, in that if you possess them, you most likely or most certainly will develop the trait/disease. However, variants such as those Angelina Jolie Pitt caries within her Brca1 gene are said to contribute very little to the genetic variance of breast cancer and ovarian cancer.