I wanted to let you know that is an extremely oft-repeated statement- homozyous Na being totally bare necked.. but it's not that simple in reality. Homozygous Na with neck patches are extremely common.. the only(visible) difference is their patches are very small, with only a few feathers on each side of the neck. Heterozygous have much larger patches with the feathers covering the lower neck and obscuring the crop area.
I'll link to examples of homozygotes with neck patches:
Note lower neck and crop area are very visible.
The difference can even be seen on day olds. Homozygotes in middle and on right side of picture; heterozygote on left. Compare the size of the neck patch & note the homozygotes also have bare patches on the face, behind the eye, between eye and beak while the heterozygote has a solidly fuzzy face.
My own picture of full siblings out of heterozygous rooster(large neck patch) & homozygous hen(very small neck patch):
I've done this sort of mating was done many times with different birds with same results: 100% chicks with naked necks in ratio of 50% like on left and 50% on right.
I've also test mated or simply did outcrosses with non-naked necked birds: large neck patch with na+= 50% naked necked chicks, 50% not naked necked. Tiny neck patch with non-naked necked= 100% naked necked chicks.
Totally bare necks seems to be due to something else. Years ago I deliberately tried to breed for completely bare necks using birds with the fewest feathers in the neck patch.. only succeeded in getting birds with as low as 1 or 2 feathers on each side.
Then in an egg trade, got a group of obviously(naked necked) mongrel stock- birds had everything possible present on at least one bird such as crests, silky feathering, leg feathering, various comb types. Several of them had completely bare necks. Breeding those together gave both not naked, small patched and totally bare necks. Crossing them with unrelated naked necked birds did not give any totally bare necks though.
Side note, crossing with pea and rose comb birds can produce homozygous looking birds.. with small neck patches, especially with pea.
No prob Henk! You're someone who knows chooks and their genetics so I jumped at the chance.. it's a battle fighting the 'only the totally bare necks are pure/homozygotes'... I'd also love to find out what it is exactly that causes totally bare necks on some birds.. my best guess is it's some kind of modifier?