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.
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