And the reason is because in certain individuals, they can actually have genetic changes or mutations that are not passed down from the mother or from the father, but actually start brand new in them, mutations that are present in the egg or the sperm at the time of conception but have not been passed down generation through generation within the family.
E iso é porque algunhas persoas poden sufrir cambios  ou mutacións xenéticas que non lles transmitiu a nai nin o pai, senón que se estrearon nelas. As mutacións están presentes no óvulo ou no espermatozoide no momento da concepción pero non se transmitiron xeración tras xeración na familia.