I've been doing some thinking on the cresting gene. I know we consider it dominant but after some breedings earlier this spring I am thinking it is actually an incomplete dominant gene. For example, my rooster over some leghorn hens is creating all crested Sapphire mixes, even though he doesn't have much of a crest. But a few of the pure Cream Legbar pullets (same dad) do not have a crest even though he does (I think I have one or two hens without crests in the breeding pen at this time). Anyone else seeing things like this?
Funny you should bring this up as I, too, have been thinking about the crested gene!
I think that the gene is incomplete dominant because it seems as though two copies make for a bigger crest...but not always. I suspect there is a modifying gene or genes (epistasis) lurking somewhere. On a competing website, there is a reference to a paper in a book: "Somes, in Chapter 6 of Crawford's
Poultry Breeding and Genetics, refers to crest as an "incompletely dominant" gene, citing the work of Hurst (1905)" but I could not turn up the original Hurst paper although his is referenced on Wikipedia under the White Gentics entry and the Crawford book is on my list but is $250 from
Amazon used so it can wait
There is also a scientific paper "The Crest Phenotype in Chicken Is Associated with Ectopic Expression of
HOXC8 in Cranial Skin" talking about crests and this also says that the gene is incompletely dominant:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3326004/ . It also says "Crest shows an autosomal incompletely dominant mode of inheritance and is associated with cerebral hernia". There is concern in the Silkie and Polish breeders about cerebral hernia (a hole in the skull so the brain is just under the skin) and there has been talk on the Swedish Flower hen about this as well. I will have to go back and re-read the paper and see what breeds they used in their study. I think the paper was out of China--quite a lot of good poultry research is done there.
If you look up a Belgian chicken breed called the Brabanconne
http://users.telenet.be/jaak.rousseau/english version/grote_hoenders/brabants_hoen.htm , the females have a decent sized crest and the males have a barely noticeable crest. It is also a single combed variety. I am intrigued by this but also realize that this is the ideal and maybe they are not showing the ones with problems, or perhaps that they have culled and over time this has resulted in more uniformity.
I have two males, both crested. One has a very small crest that showed up at around 4 weeks and seems similar to the one in the above Brabanconne reference. There is very little comb deviation and I will try to breed toward that comb and crest. The other rooster had an obvious crest tuft at hatch though I do not know if he had any boney knob that might be an indicator of a vaulted skull or cerebral hernia. His crest is very large and the comb is really deviated. That comb deviation was evident at hatch. This might be desirable if you were to double pen and go for a bouffant crest in the daughters.
I would love to hear of everyone's experience's with crests. Rinda, it sounds like your boy should be homozygous for crests if he is getting all crested over non-crested hens and it is very peculiar that he is not throwing any CL crested girls.
