http://en.wikipedia.org/wiki/Ethnic_bioweapon

I'm looking for someone with some expertise to answer this question. Can ethnic bioweapons be created in a general sense? How specific can a given population be targeted? Populations share many genes but often have them in different proportions so theoretically you may get something that kills 90% of group A and 10% of group B? Is it possible to avoid this? What are the risks of mutation? Can they be controlled etc...