Date: April 7, 2017
Source: Uppsala University
Birds show an amazing diversity in plumage colour and patterning. But what are the genetic mechanisms creating such patterns? In a new study published today in PLOS Genetics, Swedish and French researchers report that two independent mutations are required to explain the development of the sex-linked barring pattern in chicken. Both mutations affect the function of CDKN2A, a tumour suppressor gene associated with melanoma in humans.
Research in pigmentation biology has made major advances the last 20 years in identifying genes controlling variation in pigmentation in mammals and birds. However, the most challenging question is still how colour patterns are genetically controlled. Birds are outstanding as regards the diversity and complexity in colour patterning. The study published today has revealed the genetic basis for the striped feather characteristic of sex-linked barring. One example of this fascinating plumage colour is the French breed Coucou de Rennes. The name refers to the fact that this plumage colour resembles the barring patterns present in the common cuckoo (Cuculus canorus). The sex-linked barring locus is on the Z chromosome. (In chickens as well as in other birds the male has chromosomes ZZ while females have ZW).
"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. We are sure that both mutations contribute to the sex-linked barring pattern because we have also studied chicken that only carry the regulatory mutation and they show a very pale plumage with only weak dark stripes. Thus, this represents an evolutionary process in which the regulatory mutation occurred first followed by the mutation affecting the protein structure. The combined effect of the two mutations causes an even more appealing phenotype for the human eye," says Leif Andersson, Uppsala University, Swedish University of Agricultural Sciences and Texas A&M University, who led the study.