Genetics of feather pigmentation and chicken plumage colouration.

The chicken's plumage is defined by the structure and colour of its feathers. Plumage colour is a feature used in modern poultry breeding to distinguish between breeds, strains and pure lines. It is therefore important in strain security. Sex-linked genes affecting plumage colour and patterns and rate of feather development are useful in sexing of day-old chicks. Variation in plumage colour is attributable to differences in the primary and secondary colour patterns exhibited by individual birds. While the primary pattern refers to the distribution of coloured feathers in different parts of the bird's body, the secondary pattern refers to the distribution of colour on individual feathers. Although many commercial broiler and layer chicken strains exhibit solid or single colours, the chicken, like many other birds, exhibits a very wide array of plumage colour patterns, due to the presence or absence of pigments on the feathers. While some birds exhibit complete lack of pigment either in individual feathers or in all of the feathers across the body and are hence completely white, others are pigmented and exhibit a range of colours such as black, blue, brown and orange. While some have all their feathers of the same colour (solid colouration), others show a mixture of colours, which may be distributed in a specific pattern in different parts of the body such as the neck, wing and tail feathers, or have multicoloured feathers. It is now clear that all of these colour patterns are under genetic control. The development of pure lines and commercial crosses with specific colour patterns therefore requires a good understanding of the genetics of feather pigmentation and hence the inheritance of plumage colouration. This review highlights current knowledge of the genes that affect colour development and distribution in chickens as well as the pigments that colour feathers and the mechanism of their secretion. It aims to enrich our understanding of the link between the genes and the causal mutations that affect colour in chickens and the physiological pathways involved in pigment production and distribution between and within feathers of the chicken plumage.