The Cr gene for crests is incompletely dominant, so breeding a crested to a non-crested individual will result in mostly crested offspring, and those without crests will carry the gene. Those that are homozygous (Cr/Cr) will have larger crests than those heterozygous (Cr/cr).
Very interesting article, though very scientific in places, scroll down for some more plain-English explanations of Crested
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034012
Very interesting article, though very scientific in places, scroll down for some more plain-English explanations of Crested
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034012