Rose comb is the Wyandotte standard, so you cannot show a single combed 'dotte. I have read that it's okay to keep say 10% of your hen flock single combs, no single comb roos though as that would spread the gene through the flock too much. I bought BLR chicks from a private breeder who enclosed 5 "extra" chicks in the order, but told me the extras were all single combs. I can't tell the difference in the day olds, so I'm guessing he keeps whole separate flocks of single combs to enhance fertility. Maybe the fertility problem is just a 'dotte thing?