Quote: I did a bit of research afterwards, and found that there seems to be a correlation between crest size and comb size... the larger the comb the smaller the crest (not always but quite often). so that may be why roos with very large combs have very small crests...
the (informal) reasoning being that there's only so much skull to go around, so if the comb is taking up a lot of 'acreage' then the crest can only have so much more...
there were a couple breeds cited where only the hens have visible crests while the roos have extremely large combs and to have a visible crest is considered a fault. (a Belgian breed i'm not familiar with, and don't remember the name but it had a brief blurb on feathersite).
in another paper I read, it explained that the crested gene affects feather length, causing the head feathers to grow longer than normal. obviously it has been modified by selection for larger or fuller crests in some breeds, or smaller ones in others. but my understanding of some of the technical lingo was that the gene is most active when the chick is developing and cells are differentiating into their specialized components.
since we know that some developmental things can be affected by incubation problems, it would stand to reason (to me) that possibly the 'crest' cells can also be affected during incubation and possibly be limited in their expression for that reason. I have no basis on that theory, just supposition from what I have read and my knowledge of embryology and genetics from college...