i have read so many post on here about this and there were a lot of good articles and information on this topic so i decided to throw my two cents in. several years ago i picked up four sexlink pullets from a friend. he bred a rosecomb riw roo over rir hens as you know those whites are very hard to come by. both were heritage lines and happened to lay pretty good. they were the best laying chickens i have ever put my hands on and i have had isas and hy-lines but these were better. i did pick up a young roo from him also that was the same. i bred these together and through selection for the best layers continued to breed back to parent stock each breeding developing two lines one white and one red. now i prefer to breed young birds but having to go back to what i call my parent stock they slow down a little. so i perk them up a little to help the fertility. after a few generations of doing this i crossed the two lines back into each other and got as good or better than what i started with. they lay large eggs and lots of them. and yes i can color sex them although my main objective was very good layers. one key factor most people miss is put enough on ground to select the best to continue on.it takes time and space. i do not consider myself a master breeder but i have learned an awful lot since breeding chickens,horses and dogs since 1969. at present i have heritage rir in the straight comb and rose combs and working on delawares which are starting to come around and just got some light sussex . im not in the wholesale chicken business i breed these just to prove to myself i can. in putting a few thousand chickens on the ground i have learned a little but more to go.