As one of the most obvious phenotypic characters, coat color in domestic pigs is of great importance in artificial selections. Six-white-point (SWP) coat (white coat on the four feet, the head, and the end of tail but with the remaining coat being black) is one of the common pigmentation patterns being found in many different breeds of both European and East Asian domestic pigs.

Previous studies revealed that in European domestic pigs, the occurrence of SWP coat pattern are correlated with the insert mutations of MC1R gene. However, because European and East Asian domestic pigs have independent domestication origins, the mechanisms of SWP pigmentations in the latter may different with that of the former.

The research team led by Prof. ZHANG Yaping at Kunming Institute of Zoology of Chinese Academy of Sciences recently conducted a study to explore the genetic mechanisms underlying the SWP pigmentations in the Diannan small-ear (DSE) pigs from Yunnan Province, China.

In this study, to compare coat color phenotype, a total of 753 black DSE pigs and 1,224 SWP DSE pigs were sampled, and coat color of the litters of either black parents or SWP parents were observed. To analyze SWP phenotype, the whole genomes of 17 SWP pigs and 14 black DSE pigs were resequenced. The genomic reads were quality filtered and the resequencing data for each individual covered about 75% of the reference genome. The genomic regions highly differentiated between the SWP and black DSE pigs were screened.

The results inferred that the SWP coat color in Diannan small-ear pigs is likely regulated by polygenic loci, rather than the MC1R locus. Strong associations were observed at three loci (EDNRB, CNTLN, PINK1). These different loci have varying contributions to the formation of the SWP phenotype and answer approximately 20% coat color variations in DSE pigs. Moreover, a few novel candidate genes influencing coat color variation worth attention were indentified.

This study expanded knowledge on coat color evolution in DSE pigs and challenged the traditional understanding of monogenic pigmentation regulation mechanisms. It had critical directive significance in pig breeds artificial selections. The study have been published on Scientific Reports.