I have heard that you can mate sister to brother, father to daughter or mother to son with chickens and it has no side affects like other animals do. I've also heard that it should be avoided at all cost. Can someone on here please give me some advice on this subject? I have a sister and brother Marans that someone gave me and would like to produce a few chicks from them to add to my dark egg collection. Is this ok or should I not do it?