The domestic Crested Duck is a duck

Duck

Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...

 breed descended from the Mallard

Mallard

The Mallard , or Wild Duck , is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand and Australia....

. It has its appearance because it is heterozygous for a genetic mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 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
  Allele
  An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
  
   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
  Allele
  An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
  
   of this gene and die from exposed brain
  Brain
  The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
  
   without hatching, as it is lethal in homozygous form.

If a crested duck and a non-crested duck breed together, the resulting ducklings would be expected to be 50% crested and 50% non-crested.

Approximate weight (metric)

Drake	3.2 kg
Duck	2.7 kg

Miniature Crested

Drake	1.3 kg
Duck	0.9 g

See also

• Crested Duck
  Crested Duck
  The Crested Duck is a species of duck native to South America, the only member of the monotypic genus Lophonetta. It is sometimes included in Anas, but it belongs to a South American clade that diverged early in dabbling duck evolution . There are two subspecies: L...
  
  , the wild species
  Species
  In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
  
   Lophonetta specularioides
• List of duck breeds

External links

• http://www.feathersite.com/Poultry/Ducks/Crest/BRKCrestedDucks.html
• Poultryhub.org Fancy Duck Breeds - Crested Duck