Auto-sexing

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, of goose and of domestic pigeon have this characteristic. 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.
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.
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. About ten years later they produced the Legbar by crossing brown Leghorns with barred Plymouth Rocks.
Other "Cambridge" breeds later developed were:
Many other breeds were created in the same way, all making use of barred Plymouth Rocks to impart the barred gene: