Auto-sexing

a dull grey-brown hen
The Cream Legbar, an auto-sexing breed

Auto-sexing breeds of poultry 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,[1]: 53  of goose and of domestic pigeon have this characteristic.[2] The idea of such a breed is due to Reginald Punnett, who created the first auto-sexing chicken breed, the Cambar, at the Genetical Institute in Cambridge in 1928.[3]: 318 [4]: 73 

Mechanism

Unlike sex-linked 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, 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.[5] 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.[5]

The marked difference between male and female chicks is due to gene dosage of the sex-linked barring gene ('barring' (B), 'nonbarring' (b+)).[5][6] 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 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.[5][6][7]

Chickens

The concept of an auto-sexing breed of chicken is due to the geneticist Reginald Punnett, who during the First World War had already proposed the technique of cross-breeding chickens carrying the barred gene (B) with others to produce sex-linked chicks with plumage differences that could easily be distinguished.[3]: 317 

Working at the Genetical Institute of Cambridge University, he and Michael Pease cross-bred Golden Campines with barred Plymouth Rocks, resulting in the creation of the Cambar in 1928.[4]: 73  About ten years later they produced the Legbar by crossing brown Leghorns with barred Plymouth Rocks.[3]: 318 

Other "Cambridge" breeds later developed were:

  • the Brockbar, created in 1940 from buff and barred Plymouth Rocks, became extinct by about 1950[1]: 54 
  • the Brussbar, created in 1952 from light Sussex, brown Sussex and barred Plymouth Rocks[1]: 55 
  • the Dorbar, an auto-sexing heavy meat breed from Dorkings and barred Plymouth Rocks, bred from 1941 to about 1949, when development stopped[1]: 59 
  • the Rhodebar, from Rhode Island Reds and barred Plymouth Rocks, standardised in Britain in 1951; a similar cross-breed was developed in Canada[1]: 63 
  • the Welbar, not created at Cambridge but by a Devon breeder, from Welsumer and barred Plymouth Rocks;[1]: 65  and
  • the Wybar, also not created at Cambridge but by an individual breeder, from Wyandotte, Brussbar and barred Plymouth Rocks.[1]: 68 

Many other breeds were created in the same way, all making use of barred Plymouth Rocks to impart the barred gene:

References

  1. ^ a b c d e f g J. Ian H. Allonby, Philippe B. Wilson (editors) (2018). British Poultry Standards: complete specifications and judging points of all standardized breeds and varieties of poultry as compiled by the specialist breed clubs and recognised by the Poultry Club of Great Britain, seventh edition. Chichester; Hoboken, New Jersey: Wiley Blackwell. ISBN 9781119509141.
  2. ^ W. F. Hollander (1942). Auto-sexing in the Domestic Pigeon. Journal of Heredity. 33 (4, April 1942): 135–140. doi:[https://doi.org/10.1093%2Foxfordjournals.jhered.a105150 10.1093/oxfordjournals.jhered.a105150. (subscription required).
  3. ^ a b c F. A. E. Crew (1967). Reginald Crundall Punnett. 1875-1967. Biographical Memoirs of Fellows of the Royal Society 13: 309–326.
  4. ^ a b Lewis Stevens (1991). Genetics and Evolution of the Domestic Fowl, digital edition (2005). Cambridge; New York; Port Chester: Melbourne; Sydney: Cambridge University Press. ISBN 9780521403177.
  5. ^ a b c d Victoria Roberts (2008). British poultry standards: complete specifications and judging points of all standardized breeds and varieties of poultry as compiled by the specialist breed clubs and recognised by the Poultry Club of Great Britain. Oxford: Blackwell. ISBN 9781405156424. p. 53-56
  6. ^ a b Anders R. Hellström, Elisabeth Sundström, Ulrika Gunnarsson, Bertrand Bed’Hom, Michèle Tixier-Boichard, Christa F. Honaker, Anna-Stina Sahlqvist, Per Jensen, Olle Kämpe, Paul B. Siegel, Susanne Kerje1, Leif Andersson (2010). Sex-linked barring in chickens is controlled by the CDKN2A/B tumour suppressor locus. Pigment Cell and Melanoma Research. 23 (4): 521–530. doi:10.1111/j.1755-148X.2010.00700.x.
  7. ^ B. J. Dorshorst, C. M. Ashwell (2009). Genetic mapping of the sex-linked barring gene in the chicken. Poultry Science. 88 (9): 1811–1817. doi:10.3382/ps.2009-00134.
  8. ^ Janet Vorwald Dohner (2001). The Encyclopedia of Historic and Endangered Livestock and Poultry Breeds. New Haven, Connecticut; London: Yale University Press. ISBN 0300088809.
  9. ^ a b c Frederick Bruce Hutt (1949). Genetics of the Fowl, reprint edition, 2003. Blodgett, Oregon: Norton Creek Press. ISBN 9780972177030.
  10. ^ R. George Jaap (1940). Methods for producing auto sexing varieties of chicks. U.S. Egg Poultry Magazine. 46: 36–39.
  11. ^ W. F. Lamoreux (1941). The Autosexing Ancobar Journal of Heredity. 32 (7, July 1941): 221–226. doi:10.1093/oxfordjournals.jhered.a105045. (subscription required).
  12. ^ Magdalena Gryzinska, Ewa Blaszczak, Aneta Strachecka, Grazyna Jezewska-Witkowska (2013). Analysis of Age-Related Global DNA Methylation in Chicken. Biochemical Genetics 51 (7–8): 554–563. doi:10.1007/s10528-013-9586-9.
  13. ^ Fritz Schöne (2008). Bielefeler Kennhühner: Attraktiv durch Leistung und Kennfarbigkeit (in German). Geflügelzeitung 18 (2006): 6–8.

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