During the weekly genetic mini-series, we have discussed the basics of genetic inheritance in chickens. We first discussed egg color, introducing the idea of basic autosomal dominance (simple dominant and recessive) during our discussion of blue egg color. We then approached incomplete dominance as seen in blue feathering. After reviewing the basic mechanics of DNA and chromosomes, we played with the idea of sex-linkage in chickens as a result of the female being hemizygous for the Z sex chromosome which carries silver, barring, rate of feathering, and dermal melanin (also chocolate; see here.) Within these topics, we have covered the mechanisms by which all traits in chickens are inherited. Now we can simply keep these mechanisms in mind as we play with chicken colors and forms.
Genetics Mini-Series Article #7
The best article on chicken plumage is hands-down the “Basics” of chicken color on the kippenjungle/Chicken Quest site. The more time you spend exploring his website, the more you will find like this list of chicken genes or pictures of cool, instructive breeding projects. That said, I’ll summarize and simplify here.
There are two basic pigments made by animals, including birds: eumelanin, a black pigment, and phenomelanin, a red pigment. Both are forms of melanin. You see eumelanin everywhere. It is the pigment that darkens our skin to protect us from ultraviolet radiation, the fur of our dogs and cats, and the black and blues we see in chicken feathers. Phenomelanin colors our freckles, the tawny yellow of lion’s fur, and the red and gold of plumage. Both of these pigments can be inhibited to create lighter greys and browns (eumelanin), buff or blonde (phenomelanin), or even white.Other colors we see in birds and animals (also here) are created in two main ways: pigments derived from the food they eat and colors created by the play of light through structural patterns in feathers. We all know that flamingos get their fantastic pink color from their diet: The carotenoids contained in the plant life (algae) eaten by shrimp are passed up the food chain to give flamingos a color they could not create themselves. The bright blue of an indigo bunting’s feathers is really just black eumelanin, but the structure of the feather causes the light to refract in such a way as to appear bright blue. A wild-type chicken (e+, often called duckwing) has a base or ground color of phenomelanin which you can see clearly in the salmon/reddish breast of the female. You can see the black of eumelanin in the breast and tail of the male. The genetics guru at the kippenjungle/Chicken Quest site (Henk69 on forum sites) explains:
The wildtype chicken male and females have sexual dimorphic plumage color. The hen has to be camouflaged and therefor is more groundcolored than the male; she has delicate black patterning. Her neck is gold with black striping towards the shoulder, the breast is salmon colored, a kind of pheomelanin expression; the upperside is densely “stippled” on a yellow/brown background. The rooster has more bright groundcolor shades and has big black areas with green sheen on tail and wingbands. The breast is generally black; neck hackles, shoulder and saddle are red to gold. The wing triangle is golden brown in wildtype male.
Areas typically dominated by eumelain or phenomelanin can be extended. For example, the dominant trait E, or extended black, literally extends the area of eumelanin to make an entirely black bird. Buff birds are covered by an extended area of phenomelanin, diluted by inhibitors. (Interestingly, geneticists haven’t figured out what gene inhibits all of the eumelanin in a buff bird. The closest thing they know of is Colombian restriction, Co, which restricts or limits eumelanin to the hackles and tail.) Birchen (ER), wheaten (EWh), and partridge (Eb) are other patterns emphasizing (or restricting) areas of eumelanin and phenomelanin.Both eumelanin and phenomelanin can be enhanced by other genes, affecting their appearance. The black eumelanin can be enhanced by other genes (melanizers) to become shinier. While a shiny area of eumelanin often takes on a beetle-green sheen, the presence of autosomal red can make the sheen purple as we sometimes see in Sumatras. A form of melanizer, Melonic (Ml),and the pattern gene (Pg) concentrate the black pigment in certain areas of the feather to create penciling, lacing, and spangling. Charcoal (cha) also enhances black pigment. Genes that enhance phenomelanin make a vivid red or dark red of a Rhode Island Red which relies on Mahogany (Mh). Both eumelanin and phenomelanin can also be inhibited. Dominant white (I) and recessive white (c, colorless) inhibit the expression of any pigment. Inhibiting in a certain pattern results in mottling (Mo) or barring (B). Inhibiting overall can result in a lighter color from less-dense pigment: black is lightened to blue (Bl), chocolate (choc), or dun (Id, 2 copies khaki); red/gold phenomelanin is diluted with Di (dilute), Ig (lemon), or Cb (champagne blonde) and completely inhibited by S (silver). Lavender (Lav) acts on both pigments, diluting eumelanin to lavender and phenomelanin to isabel (also here). For more information, please read the “Basics” article linked above. There are also fantastic articles and book previews on ChickenColours.com. To see amazing works of living art, go to One Earth Farm’s websiteand browse their project pages, including the now well-known Buff Laced Brahma.