In poultry standards, solid white is coloration of plumage in chickens (Gallus gallus domesticus) characterized by a uniform pure white color across all feathers, which is not generally associated with depigmentation in any other part of the body.

Color is an important feature of most living organisms. In the wild, color has great significance affecting the survival and reproductive success of the species. The environmental constraints which lead to the specific colors of birds and animals are very strong and individuals of novel colors tend not to survive. Under domestication, mankind has transformed all the species involved which have thus been freed from environmental pressures to a large extent. Early color variants were mostly selected for utility reasons or religious practices. In more recent centuries color varieties have been created purely for ornament and pleasure, fashion playing a surprisingly large part in their development. A bewildering array of colors and patterns can now be found in the domestic fowl.Sheppy, A. 2011 The colour of domestication and the designer chicken. Optics & Laser Technology Volume 43, Issue 2, pp. 295–301. 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. And there are many other breeds better known by their colored varieties, which also have a solid white variety, such as Plymouth Rock, Orpington, Rhode Island Red, Jersey Giant and others.Hutt, F.B. Genetics of the fowl. McGraw-Hill Book Co. N.Y. 1949.Somes, R. G. International Registry of Poultry Genetic Stocks. A Directory of Specialized Lines and Strains, Mutations, Breeds and Varieties of Chickens, Japanese Quail and Turkeys. Storrs Agricultural Experiment Station, The University of Connecticut, Storrs, Bulletin #460, (1981).

Description

Chicks down color of solid white chicken breeds can vary from a light creamy white, through different yellow shades, to a toasted orange. 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.

History

Most chicken plumage color genetic factors were manipulated during domestication by selection and crossings, which led to the modern chicken breeds, but there are no historical records of when or where the first chicken breeds with solid white plumage arose. In the creation of new white breeds, white color have been sometimes introduced from breeds of solid white plumage. Rhode Island White arose from the work of J. Alonzo Jocoy of Peacedale, Rhode Island, which began in 1888. Developed through crosses of Partridge Cochins, White Wyandottes, and the rose comb type of White Leghorn, it was solidified as a breed by 1903. And it was first accepted into the American Poultry Association's Standard of Perfection in 1922. Moderately popular up until the 1960s, it is now a relatively rare fowl.

On the other hand, there is not a unique genetic mutation for solid white plumage color. There are two very well known autosomal major mutations leading to solid white plumage color, but also a number of complementary mutations properly combined may reduce or restrict pigment with a sufficient intensity to produce a final solid white plumage color, even in the absence of the major mutations for white. Most varieties of solid white plumage chickens belong to some of the first two major mutations leading to solid white plumage color. These are commonly regarded as "dominant white" and "recessive white" according to the major mutation involved. The term "dominant white" has also been applied in genetic literature to a mutation producing white coat color in horses.

Four different recessive albino or albino-like mutations which also produce white plumage color in the chicken were also reported in literature, but those are not typical of any breed of chicken, and may be associated to a reduced perinatal viability or a deficient vision.

Dominant white

Dominant white was one of the first traits in aviculture which proved to be inherited according to the Mendelian laws, when in 1902 BatesonBateson, W. 1902 Experiments with poultry. Repts. Evol. Comm. Roy. Soc. I, 87-124. found that the cross of White Leghorns x Indian Games (or its reciprocal) gives F1 chicks with a white or a black spotted ashy white down. And that the F2 gives light and dark chicks in the 3:1 Mendelian proportion, which was confirmed by Hurst in 1905,Hurst, C.C. 1905 Experiments with poultry. Repts. Evol. Comm. Roy. Soc. II, 131-154. Bateson and Punnet in 1906Bateson, W. and Punnet, R.C. 1906 Experimental studies in the physiology of heredity, Poultry. Repts. Evol. Comm. Roy. Soc. III, 11-30. and many others. The symbol I (inhibitor of black) to identify this mutation was introduced by Hadley in 1913.Hadley, P.B. 1913 Studies on inheritance in poultry. I. The constitution of the White Leghorn breed, Rhode Island Agr. Expt. Sta. Bull. 155. Although homozygotes I/I have always a solid white plumage color, heterozygous I/i+ chicks are generally black spotted, while the presence of black or partially black feathers on a whitish adult plumage is very common.

Recessive white

Solid white varieties of Dorkings, Plymouth Rocks, Wyandottes, Minorcas, Orpingtons and other breeds are regarded as recessive whites because their white is completely recessive to any other color. Both kinds of white plumage: "dominant white" and "recessive white" are phenotypically identical in adult phase, and can only be distinguished from each other by means of a progeny test. In 1906 and 1908 Bateson and PunnetBateson, W. and Punnet, R.C. 1908 Experimental studies in the physiology of heredity, Poultry. Repts. Evol. Comm. Roy. Soc. IV, 18-35. demonstrated that White Dorkings are homozygous for an autosomal recessive mutation which prevents appearance of color. They assigned to this mutation the symbol c, as being recessive from the normal allele (C+, chromogen) which allows normal plumage color development. This same kind of white plumage color was found by Bateson and Punnet in Rose Comb Bantam and in White Wyandotte. It was also found in White Cochin by Davenport in 1906,Davenport, C.B. 1906 Inheritance in poultry. Carnegie Inst. Publication #52. in White Langshan by Goodale in 1910,Goodale, H.D. 1910 Breeding experiments in poultry. Proc. Soc. Exptl. Biol. Med. 7, 178-179. in White Plymouth Rock by Hadley in 1914,Hadley, P.B. 1914 Studies on inheritance in poultry. II. The factor for black pigmentation in the White Leghorn breed. Rhode Island Agr. Expt. Sta. Bull. 161. and in other breeds.

"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. White Plymouth Rock chickens carry a considerable mixture of genes taken from other breeds different from the original Barred Plymouth Rock from which the white variety originates.

Albinism and partial albinism

Dominant and recessive major solid white plumage varieties are not albinos, but just white chickens in which melanin is limited to eyes. In the ornithological literature there are many reports about totally or partially albino birds, but most of them are not studied genetically.

In 1933 WarrenWarren, D.C. 1933 Inheritance of albinism in the domestic fowl. Journal of Heredity 24:379-383. described in White Wyandotte a kind of complete albinism caused by an autosomal recessive mutation to which he assigned the symbol a. As the White Wyandotte birds were of a solid white plumage color, albinos could only be recognized by the brilliant red of their eyes. Those albinos had such a deficient vision that newborn chicks had difficulties to find the feeders, while adult females had difficulties to find the provided trap-nests . They were all very sensitive to sun light and preferred to remain indoors.

Light microscopic histology of the retinal pigment epithelium of autosomal albinos was done in the original study by Warren, but subsequent light or electron microscopic studies of autosomal albino eyes or feathers have not been reported. The histology of the iris showed no evidence of pigmentation. At the ultra-structural level, small, spherical, poorly pigmented granules were seen in autosomal albino retinal melanocytes.

In 1940 WarrenWarren, D.C. 1940 Inheritance of pinkeye in the fowl. Journal of Heredity 31:291-292. described a different autosomal recessive mutation known as "pink eye" (pk) that severely reduce pigmentation in the eyes, but only dilutes the pigment in the plumage, so this mutation does not produce a solid white color. The ultra-structure of "pink eye" melanocytes from both the eyes and feathers of embryo chicks and adults has been extensively defined.Brumbaugh, J.A. 1968 Ultrastructural differences between forming eumelanin and pheomelanin as revealed by the pink-eye mutation in the fowl. Develop. Biol. 18:375-390.Brumbaugh, J.A., Bowers, R. and Chatterjee, G. 1973 Genotype-substrate interactions altering Golgi development during melanogenesis. Pigment Cell 1:47-54.Brumbaugh, J.A. and Lee, K. 1975 The gene action and function of two dopa oxidase positive melanocyte mutants of the fowl. Genetics 81:333-347Brumbaugh, J.A. and Lee, K. 1976 Types of genetic mechanisms controlling melanogenesis in the fowl. Pigment Cell 3:165-176

In 1941 Mueller and HuttMueller, C.D. and Hutt, F.B. 1941 Genetics of the fowl. 12. Sex-linked imperfect albinism, Journal of Heredity. 32, 71-80. reported a sex-linked partial albinism in Barred Plymouth Rock due to a simple sex-linked recessive mutation. The same mutation was later found in another flock of Barred Rocks and in White Leghorn. Affected birds had as good vision as normal ones.