No matter how small it is, almost every aspect of biology’s life is under the close watch of evolutionary selection. And the influence of selection could show in different ways. For example, directional selection is a mode in which the best man wins, which means a single phenotype will be favored and the allele frequency will continuously shift in one direction. But one the other hand, there also has mode which encourages diversities, such as balancing selection. In this mode, multiple alleles will be actively maintained in the gene pool of a population at frequencies above that of gene mutation. In this way, genetic polymorphism will be conserved.
One of the straight forward examples of polymorphism is the coat color of domestic dogs. Compared with that observed on their ancestors, the variable coat color of domestic dogs, such as black, yellow, red, gray and between, are overwhelming. “And also because of this colorful diversity, it has become an ideal start point for us to dig the secrets of artificial selection”, Dr. WANG Guodong (Kunming Institute of Zoology, the CAS) said.
In collaboration with Kunming Police Dog Base, the Ministry of Public Security, Dr. WANG and his colleagues has conducted an analyze of two stable populations of Kunming dog, the Wolf Black (WB) and Back Black (BB). “Each of these two populations was bred separately by a random mating approach during the past 16 years, which makes them an excellent resource to examine the evolutionary process that occurs to color genes under recent domestication process”, according to Dr. WANG.
Coat color is generated by melanocytes, which synthesize pheomelanin (a red or yellow pigment) or eumelanin (a black or brown pigment) through the pigment type-switching pathway, and is regulated by three genes in dogs: MC1R (melanocortin receptor 1), CBD103 (b-defensin 103), and ASIP (agouti-signaling protein precursor). By resequencing those three pivotal genes of the two Kunming dog populations and analyzing these sequences using population genetic approaches, the results showed that MC1R undergoes balancing selection in both dog populations during the recent domestication and breeding. Well, in contrast, no similar results were observed for CBD103 or ASIP. Moreover, additional analyses showed that quite different haplotype distributions exist at the MC1R locus in the WB and BB populations, although both populations have a high heterozygosity caused by balancing selection.
In a word, Dr. WANG’s recent study suggests that MC1R accounts for the coat color difference between these two populations and that the different compositions of the MC1R haplotypes might be responsible for the among-population differentiation in coat color patterns between the two Kunming dog populations.
The main findings of this study have been published on PLoS One (http://dx.plos.org/10.1371/journal.pone.0055469).
(By Su-Qing Liu)
