( thanks NN breeder for the info and for getting me hooked on these birds.)
Either 50% of the chicks will have naked necks(in both sexes).. or 100% of them. It depends on whether he has one or two copies of the naked neck gene. Two would make heterozygous.

If your rooster either has a totally bare neck or has a tiny bow tie with only few feathers, you might expect to get 100% naked necked chicks. If he has a large clump (big bow tie) with the feathers covering "a good bit" of the neck, he's probably not pure.. expect 50% naked necked chicks.

You'll know once you hatch at least 15-20 chicks.. if any chick hatches without a naked neck, it is proof he has just one copy of the naked neck gene. Even if it's just 2-5 out of 15. However if you hatch at least 20 and all have naked necks, the rooster is pure for it and a good choice to keep for future breeding if he is also good in other ways.

Also, if you plan on breeding for naked necks, do not save the non-naked necked chicks.. they don't have the gene in them at all. That is unless the bird has something you like and want to introduce into your naked necks. The naked neck gene is dominant which means if the bird has it, you see it.. if bird doesn't SHOW it, it doesn't have the gene at all. Simple as that.

To keep NNs close to standard outcrosses must be made. If you keep a feather necked rooster and hen that you like the looks of out of some of the hatches the percentage of NNs will go up to about a 75/25 split.

But if you were to get a homozygous rooster and breed back to a NN hen of course it would be 100% NNs. It has been my experience that once you accomplish this the thing to do would be to line breed them. If you try to do that, they will start to lose body type and the dead in the shell rate goes way up. What they are trying to do is to revert back to the Madagascar Game form from which they were originally bred from.

Here is a pic of a stuffed specimen that is in a museum in Northern France.


As far as the Nana or NaNa genes the general rule used to be that if a chick had a totally bare neck it stood a very good chance of being homozygous (NaNa) and those could pop up any time. It seems that the genes are not just dominant or recessive, it seems that in some birds the genes can be more dominant or more recessive. Like breeding two NNs and getting feather necked birds.
Breeding this breed is fun and challenging. Color, feathering and body type will differ in every hatch. And now that I think of it I have bred more bare necked hens then roosters over the years.