e/Crested Duck (domestic breed)

Information
has gloss	eng: The domestic Crested Duck is a duck breed descended from the Mallard. It has its appearance because it is heterozygous for a genetic mutation causing a deformity of the skull. As a result, when a pair of crested ducks breed, the young sort out in the usual 1-2-1 ratio:- * 25% are homozygous for the normal allele of this gene and so have no crest and if bred together their offspring will never have a crest. * 50% are heterozygous for this gene and hatch with a crest of varying sizes. * 25% are homozygous for the crested allele of this gene and die from exposed brain without hatching, as it is lethal in homozygous form.
lexicalization	eng: Crested Duck
instance of	c/Domesticated birds