Solid white (chicken plumage)
In more recent centuries color varieties have been created purely for ornament and pleasure, fashion playing a surprisingly large part in their development.
[1] In the last decades white plumage color has become essential for the efficient processing of broilers and most types of meat-type poultry.
Slaughterhouses and meat processing plants require poultry with a white or very light undercolor to produce carcasses without the typical "hair", which colored chickens have, that necessitates singeing after plucking.
There are several chicken breeds having solid white as the most typical plumage color, such as Leghorn, Dorking, Bresse Gauloise, Polish, Wyandotte and others.
[2] In adult phase, the entire surface of the plumage is pure white due to the absence of melanin pigmentation in all parts of the feathers.
The absence of melanin in the plumage of solid white chicken breeds does not affect other body structures, except in the case of the albinos, which are easily recognized by their pink eye color.
In 1906 and 1908 Bateson and Punnet[6][8] demonstrated that White Dorkings are homozygous for an autosomal recessive mutation which prevents appearance of color.
"Recessive white" chickens may be potentially black barred or of some other color pattern, but does not reveal this, unless they are submitted to a progeny test.
In 1933 Warren[12] described in White Wyandotte a kind of complete albinism caused by an autosomal recessive mutation to which he assigned the symbol a.
At the ultra-structural level, small, spherical, poorly pigmented granules were seen in autosomal albino retinal melanocytes.
In 1983 Brumbaugh, Bargar and Oetting[19] reported a third recessive allele at the C pigment locus, to which they assigned the symbol ca.
Concomitant electron microscope studies of both retinal and feather melanocytes showed that both mutant alleles c and ca are citochemically tyrosinase negative, possess hypertrophied Golgi systems and contain numerous vesicles that appear to be incompletely formed, unpigmented granules.
At the ultra-structural level, small, spherical, poorly pigmented granules were seen in autosomal albino retinal melanocytes.
Albinos exhibit shorter down length, reflecting a general state of immaturity and retardation of neonatal development, higher incidence of subcutaneous haemorrhage and inflammation, increased incidence of yolk sac protrusion and slower growth rate and smaller body size than colored chickens.
[20][21] The numerous alterations associated with partial albinism in the fowl are difficult to explain merely considering C locus only the structural gene of tyrosinase.
[2] In other words, homozygous I/I chickens have solid white plumage regardless of the other major or complementary mutations present in the individuals, but without effect on the melanin of the eye.
As in both breeds it was not evident the presence of "dominant white" mutation, the results were completely unexpected until its revelation by the progeny tests.
It is of importance to the meat breeding industry to know the magnitude of the depression in growth rate caused by the recessive white genotype in the commercial stocks.
[35] Original wild plumage color of turkeys (Meleagris gallopavo) is bronzed, but solid white plumage color due to an autosomal recessive allele (c) in homocygosis[3] is the most frequent phenotype, extended by domestication and imposed by the requirements of meat processing plants.
Hutt and Mueller (1942)[36] found a partial albinism in bronzed turkeys determined by a simple sex-linked gene, which is semi-lethal during incubation period or later.
Solid white feather is due to an autosomal recessive allele (wh) in homocygosis, although some birds may exhibit a few black spots.
This mutant color gene produces a white quail with dark eyes when homozygous and two-color pattern known as "tuxedo" when heterozygous.
This kind of albinism eliminates melanin and the structural color found in the gene carriers, leaving untouched lipochrome pigments.
McIlhenny(1940)[45] found a type of albinism in the northern mockingbird (Mimus polyglottos L., Mimidae) which is inherited as a simple autosomal recessive.
