Crested (Poly-genic)

This mutation is poly-genic and results in the feathers on a budgie's head to grow in a different direction, which causes disturbances in the feathers in a circular pattern. It almost looks as if someone is blowing on the feathers, causing them to separate in different directions, leaving a tiny featherless patch right in the middle. The mutation has 3 visual types; tufted, semi-circular, or full circular crested. The mode of inheritance is not well understood, but two genes are thought to be involved; crest initiating gene and crest determining gene. These genes are thought to be semi-dominant, but with low penetrance and high variability. The tufted phenotype results if the bird is heterozygous for both genes, semi-circular results when the bird is heterozygous for the initiating gene and homozygous for the determining gene, and finally, the full circular crest results when the bird is homozygous for the initiating gene and homo- or heterozygous for the determining gene. A bird is considered to be "crest-bred" if it has one of the crested genes but not the other. This is not quite the same as being split for a mutation.