Before revision:  Furthermore, we establish constructions, again based on the stratified ancestral selection graph, that allow to trace back the ancestral lines into the distant past and obtain explicit results about the ancestral population in the case of unidirectional mutation.
After revision:  Furthermore, with the help of the stratified ancestral selection graph, that allow to trace back the ancestral lines into the distant past and obtain explicit results about the ancestral population in the case of unidirectional mutation.