Auto-sexing breeds of

poultry Poultry () are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes (which includes chickens, quails, ...

are those in which the sex of newly-hatched chicks can be determined from the colour and markings of the down. Some breeds of

chicken The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adu ...

, of

goose A goose ( : geese) is a bird of any of several waterfowl species in the family Anatidae. This group comprises the genera ''Anser'' (the grey geese and white geese) and '' Branta'' (the black geese). Some other birds, mostly related to the ...

and of

domestic pigeon The domestic pigeon (''Columba livia domestica'' or ''Columba livia'' ''forma'' ''domestica'') is a pigeon subspecies that was derived from the rock dove (also called the rock pigeon). The rock pigeon is the world's oldest domesticated bird. M ...

have this characteristic. The idea of such a breed is due to

Reginald Punnett Reginald Crundall Punnett FRS (; 20 June 1875 – 3 January 1967) was a British geneticist who co-founded, with William Bateson, the ''Journal of Genetics'' in 1910. Punnett is probably best remembered today as the creator of the Punnett ...

, who created the first auto-sexing chicken breed, the Cambar, at the Genetical Institute in

Cambridge Cambridge ( ) is a College town, university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cam ...

in 1928.

Mechanism

Unlike

sex-linked Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome). In humans, these are termed X-linked recessive, ...

hybrids, such as 'red sex-links' or 'black sex-links', the Legbar is an auto-sexing breed. Several other auto-sexing breeds or auto-sexing varieties of breeds exist, such as Plymouth Rock,

Bielefelder Kennhuhn The Bielefelder Kennhuhn or Bielefelder is a German breed of domestic chicken. It was developed in the area of Bielefeld in the 1970s by Gerd Roth, who cross-bred birds of Malines and Welsumer stock with American Barred Rocks to create the ...

, Niederrheiner, and Norwegian Jærhøns. Most breeds that end with -bar, such as Welbar, Rhodebar, Brussbar or Wybar, are auto-sexing as well. The importance that auto-sexing plays in the Legbar breed is also reflected in the fact that, next to a standards for the adult birds, the down colour and patterns are also standardised. Day-old male chicks can be distinguished from day-old female chicks by the down colour and the pattern they form. Female Legbar chicks in general have a broad very dark brown stripe extending over the head, neck and rump and a clear eye barring. The edges of the stripe are clearly defined and should not be blurred and blending with the ground colour, which is dark brown. A light head spot should be visible but is usually small. The male Legbar chicks in contrast have a much paler down shade and the pattern is blurred and washed out from head to rump. The marked difference between male and female chicks is due to gene dosage of the sex-linked barring gene ('barring' (B), 'nonbarring' (b+)). This gene is located on the Z-Chromosome of birds. Birds have different sex-chromosomes (Z and w) and a different sex-determination system compared to mammals (X and Y). Male birds have therefore two Z-chromosomes while female birds have a Z- and a dwarfed w-chromosome. This means that

phenotypically In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...

barred cocks can either have the B/B or the B/b+ genotype, while a barred hen always has to have a B/- genotype. The colour-sexing of Legbar chicks, however, is only possible because the male chicks have a double dose of the sex-linked barring gene (genotype B/B), while the female chicks only have a single dose (genotype B/-), resulting in the observed down colours.

Chickens

The concept of an auto-sexing breed of chicken is due to the geneticist

, who during the

First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

had already proposed the technique of

cross-breeding A crossbreed is an organism with purebred parents of two different breeds, varieties, or populations. ''Crossbreeding'', sometimes called "designer crossbreeding", is the process of breeding such an organism, While crossbreeding is used to main ...

chickens carrying the barred gene (B) with others to produce

sex-link Sex-links are crossbred chickens whose color at hatching is differentiated by sex, thus making chick sexing an easier process. Sex-links come in several varieties. As hybrids of laying or dual-purpose breeds infused with extra vigor via heter ...

ed chicks with plumage differences that could easily be distinguished. Working at the Genetical Institute of

Cambridge University The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209 and granted a royal charter by Henry III of England, Henry III in 1231, Cambridge is the world' ...

, he and Michael Pease cross-bred Golden Campines with barred

Plymouth Rock Plymouth Rock is the traditional site of disembarkation of William Bradford and the ''Mayflower'' Pilgrims who founded Plymouth Colony in December 1620. The Pilgrims did not refer to Plymouth Rock in any of their writings; the first known writt ...

s, resulting in the creation of the Cambar in 1928. About ten years later they produced the

Legbar The Legbar is a rare British auto-sexing breed of chicken. It was created in the early twentieth century by Reginald Crundall Punnett and Michael Pease at the Genetical Institute of Cambridge University. They cross-bred American barred Pl ...

by crossing brown Leghorns with barred Plymouth Rocks. Other "Cambridge" breeds later developed were: * the Brockbar, created in 1940 from buff and barred Plymouth Rocks, became extinct by about 1950 * the Brussbar, created in 1952 from light Sussex, brown Sussex and barred Plymouth Rocks * the Dorbar, an auto-sexing heavy meat breed from Dorkings and barred Plymouth Rocks, bred from 1941 to about 1949, when development stopped * the Rhodebar, from

Rhode Island Red The Rhode Island Red is an American breed of domestic chicken. It is the state bird of Rhode Island. It was developed there and in Massachusetts in the late nineteenth century, by cross-breeding birds of Oriental origin such as the Malay wit ...

s and barred Plymouth Rocks, standardised in Britain in 1951; a similar cross-breed was developed in Canada * the Welbar, not created at Cambridge but by a Devon breeder, from

Welsumer The Welsummer or Welsumer is a Dutch breed of domestic chicken. It originates in the small village of Welsum, in the eastern Netherlands. It was bred at the beginning of the twentieth century from local fowls of mixed origin: Rhode Island ...

and barred Plymouth Rocks; and * the Wybar, also not created at Cambridge but by an individual breeder, from Wyandotte, Brussbar and barred Plymouth Rocks. Many other breeds were created in the same way, all making use of barred Plymouth Rocks to impart the barred gene: * The American California Grey was bred in the 1930s in Modesto, California. * In about 1936 Arend L. Hagedoorn introduced the barred gene to

Barnevelder The Barnevelder is a Dutch breed of domestic chicken. It resulted from cross-breeding between local Dutch chickens and various "Shanghai" birds imported from Asia to Europe in the later part of the nineteenth century; these may have been of Brah ...

s and to brown Leghorns. * In 1940 R. George Jaap produced the Oklabar by crossing dark Cornish with barred Plymouth Rocks. * By 1941 the Ancobar had been bred from mottled

Ancona Ancona (, also , ) is a city and a seaport in the Marche region in central Italy, with a population of around 101,997 . Ancona is the capital of the province of Ancona and of the region. The city is located northeast of Rome, on the Adriatic ...

s and barred Plymouth Rocks, by W. F. Lamoreux at

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...

Ithaca, New York Ithaca is a city in the Finger Lakes region of New York, United States. Situated on the southern shore of Cayuga Lake, Ithaca is the seat of Tompkins County and the largest community in the Ithaca metropolitan statistical area. It is named ...

. * The Polbar was created between 1946 and 1954 by Laura Kaufman, who crossed the native Polish Green-legged Partridge breed with barred Plymouth Rocks. * The German

, developed in the 1970s in the area of

Bielefeld Bielefeld () is a city in the Ostwestfalen-Lippe Region in the north-east of North Rhine-Westphalia, Germany. With a population of 341,755, it is also the most populous city in the administrative region (''Regierungsbezirk'') of Detmold and the ...

Nordrhein-Westfalen North Rhine-Westphalia (german: Nordrhein-Westfalen, ; li, Noordrien-Wesfale ; nds, Noordrhien-Westfalen; ksh, Noodrhing-Wäßßfaale), commonly shortened to NRW (), is a state (''Land'') in Western Germany. With more than 18 million inhab ...

from Malines,

and barred Plymouth Rocks.

References

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The Autosexing Ancobar
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Oxford: Blackwell. {{ISBN, 9781405156424. {{nobreak, p. 53-56 Poultry breeds
Poultry farming Bird colours