If I may interject....there is absolutely nothing wrong with breeding siblings, cockerels to their dams, Cocks to their daughters...If the breeder knows his/her stock and knows the purpose of the breeding...not just to produce more chicks.
I didn't say there was, it's just that a lot of people consider breeding siblings to be taboo. Believe me, I've met some newbies who think breeding siblings will result in 3 legs and scissor beaks. I try to limit breeding siblings to one generation, beyond that, I try to stick with line breeding (child to parent).