So, we know that in chicken genetics, the dam's (hen) genes control the genders of the chicks. That being said, I believe it would it be possible to isolate this trait to develop a line of chickens, well, hens anyway, that produce female heavy clutches. How many clutches do you think would have to be set by a each hen to determine her gender quotient? A dozen? Then, once you find a hen or two that seem to favor female clutches, her daughters could be screened for that trait, so on and so forth. It would be a dandy trait to work towards in harder to sex breeds like silkies.