New research has focused on the plumage color of the French breed Coucou de Rennes. The chicken is named after its plumage color resembling the barring patterns present in the common cuckoo (Cuculus canorus). The plumage relates to a sex-linked barring locus found on the Z chromosome. (In birds the male has chromosomes ZZ while females have ZW, in contrast to the XY sex-determination system in humans).
The Coucou de Rennes is an historic Breton breed. It is fairly unsociable bird that ideally needs plenty of space, although it thrives in a variety of weather conditions. The barring that makes the bird so distinctive may have evolved to provide camouflage or to act as a signal of individual quality.
With the gene investigation, principal scientist Leif Andersson, Uppsala University, Swedish University of Agricultural Sciences and Texas A&M University, explains: “Our data show that sex-linked barring is caused by two independent mutations that act together. One is a regulatory mutation that increases the expression of CDKN2A. The other changes the protein sequence and makes the protein less functionally active.” The reason the researchers are so sure about these genes is because they have studied other chickens that show a very pale plumage with only weak dark stripes. The two genes in question are the variants.
Another breed of chicken, the White Leghorn, also has the two independent mutations working together. However, sex-linked barring is not apparent because these chickens also carry a dominant gene white color which eliminates all pigment production and masks the effect of sex-linked barring.
CDKN2A, also known as cyclin-dependent kinase Inhibitor 2A, is a gene expressed in many tissues and cell types. An interesting fact about the sex-linked gene mutations is that both mutations affect the function of CDKN2A, a tumor suppressor gene associated with melanoma in humans. Research into human genetics has shown that mutations that inactivate CDKN2A are the most common explanation for familiar forms of melanomas in humans. This is a completely opposite effect to what is happening with the chickens (plumage variations).
Then research shows how domestic animals are useful as models for evolutionary processes in nature and that more can be learned from similar studies.
The research is reported to the publication PLOS Genetics. The research paper is “The evolution of Sex-linked barring alleles in chickens involves both regulatory and coding changes in CDKN2A.”
