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 Plymouth Rock birds with brown Leghorns and created the gold and silver colour varieties. Pease created a cream Legbar by cross-breeding these with white Leghorns; later crossing with Araucanas caused this to have a crest and to lay blue or blue-green eggs.
History.
The Legbar was the second auto-sexing chicken breed created by Prof. Punnett and M. Pease at the Genetical Institute in Cambridge, after the Cambar, which was created in 1929 by crossing barred Plymouth Rock with gold Campine.
The aim was to create an autosexing utility breed with a focus on egg laying, where male and female day old chicks could easily be sexed by their colour. To achieve this Punnet and Pease used a crossing programme with excellent egg layers, the Leghorn and the barred Plymouth Rock. The barred Plymouth Rock was used to introduce the sex-linked barring gene ('barring' (B)) into the Leghorn. By crossing brown Leghorn and barred Plymouth Rock the gold Legbar was created and standardised in 1945. The silver Legbar followed in 1951. It had been created by crossing the gold Legbar with white Leghorn and silver Cambar.
The cream Legbar were standardised in 1958 but nearly died out in the 1970s as blue eggs were not in demand. They were created by crossing gold Legbar with white Leghorn and cream-coloured Araucana chicken. The Araucanas introduced the dilute cream gene ('inhibitor of gold' (ig)), as well as the crest and the blue eggs into this variety.
Characteristics.
The appearance of the Legbar is similar to that of a barred Leghorn. The cream Legbar possesses in contrast to the gold Legbar and the silver Legbar a crest due to its Araucana blood. The cocks weigh between 2,7 - 3,4 kg (6.0 - 7.5 lbs) and the hens weigh between 2,0 - 2,7 kg (4.4 - 6.0 lbs).
The Legbar cock is a muscular bird with a wedge shaped body which has a prominent breast and is wide at the shoulders but tapers slightly towards the root of the tail. It carries itself sprightly and alert. The back is long and flat while the moderately full tail is carried at 45°to the back. The large wings are carried tightly and well tucked up. The fine head has a strong yellow- or horn-coloured beak and a large erect bright red single-comb with five to seven even spikes. The crest of the cream Legbar is small and compact and carried well back from the red or orange eyes, falling off the back of the head below the extended comb. The face is red and smooth with smooth and pendant cream or opaque white ear-lobes. The red wattles are long and thin and the neck is long and well feathered. The yellow legs are moderately long, strong, and free of feathers and the four toes are straight and well spread. The birds have a plumage of silky texture which is free from coarse or excessive feathers.
The female has general characteristics similar to that of the male, allowing for the natural differences between sexes. The single comb however can be either erect or falling gracefully over to either side of the face without obstructing the eyesight and the tail is carried at a lower angle. The crest of the female cream Legbar is somewhat fuller and larger than that of the male, but should never be so full as to obstruct the eyes. The legs and feet of female gold Legbars or silver Legbars can be either yellow, orange or light willow.
Colours and varieties.
The Legbar has three colour varieties: gold, silver and cream. The cream Legbar has a crest and lays blue to blue-green eggs. The Legbar used to be under the care of the rare breeds society, however since the formation of the Autosexing Breeds Association (ABA) it now falls under their care. This means it can no longer compete in rare breed classes at shows and must now compete in the Soft Feather, Light class, where no more specific classes are available.
The standards of the 'Bantam Legbars' are similar to those of the large fowl. 
Males weight 850 g (30 oz) and females weight 620 g (22 oz).
Use.
The Legbar was bred as a auto-sexing layer breed. Hens may give some 180-200 eggs per year.
Autosexing.
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. 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 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 (genoype B/B), while the female chicks only have a single dose (genoype B/-), resulting in the observed down colours.