It is impossible to accurately trace the genes of Lara Dorren. The fates of entire generations are lost to time, their picture further distorted by unclear lineages, bastard children, intentional historical falsification and a simple lack of records. In many cases, Elder Blood is too thin and has lost its power.
Moreover, not every Source attributes their magical skills to the presence of Lara's genes. A few, in whom the mutation has occurred, are marked by extraordinary abilities. They are able to travel through time and space and possess certain magical abilities. These talents are, however, wild and uncontrolled, manifesting themselves in times of stress or strong emotions, surprising even their possessors.
History knows of travelers flung far in time and space by their own abilities. That is why the Brotherhood of Sorcerers should take special care of Source-children, raise them under its watchful eyes.