It is something like the NN gene, in being a dominant type gene. Let's use NN for pure NN gene, Nn for not pure and nn for a feather neck.
If you breed a NN roo, then all of the chicks will have naked necks, no matter what the hens are- NN, Nn or NN. You could even guarantee 100% naked neck chicks if you used a NN roo over barred rocks. This sounds like pure breeding but far from it.
Nn with Nn, 75% of chicks will have naked necks. That's most of the chicks.
Nn roo bred with NN and Nn hens, there can be very few fuzzy necks with some batches seeming to throw all naked neck chicks.
Now with the O gene for the blue eggshell gene....
OO roo over any hens- all daughters will lay colored eggs. Again no matter what the hens are.
Oo roo bred with Oo hens- 75% of chicks will be OO or Oo.. with 25% being oo but the special problem.. you cannot tell if the cockerels are what.. and 12.5 chance(is that right? not exactly a math wizard here) of getting an oo pullet. That percentage will be even lower if the group is say, Oo rooster with a mixture of Oo and OO hens. It's this way that 'o' gene can float down undetected.
Evidence of Oo breeder birds will really pop up if they are bred with non-colored eggers. For example:
Oo rooster or hen bred with oo hen= only half of the daughters would lay colored. This can be a shock after the very same roo had been bred with Oo or OO hens and seemingly 100% colored egg daughters out of those.
