436 Journal of Heredity, 2021, 436–442 doi:10.1093/jhered/esab034 Special Issue Article © The Author(s) 2021. Published by Oxford University Press on behalf of The American Genetic Association. All rights reserved. For permis- sions, please e-mail: journals.permissions@oup.com Special Issue Article Genetic Background of the Polish Primitive Horse (Konik) Coat Color Variation—New Insight into Dun Dilution Phenotypic Effect Jakub Cieslak , Samantha Ann Brooks , Lukasz Wodas, Weronika Mantaj, Alicja Borowska, Joanna Helena Sliwowska, Kamil Ziarniak, and Mariusz Mackowski From the Horse Breeding Unit, Department of Genetics and Animal Breeding, Poznan University of Life Sciences, Wolynska 33, 60-637 Poznan, Poland (Cieslak, Wodas, Mantaj, Borowska, and Mackowski); the Department of Animal Sciences, UF Genetics Institute, University of Florida, Gainesville, FL 32611-0910, USA (Brooks); the Laboratory of Neurobiology, Department of Zoology, Poznan University of Life Sciences, 60-625 Poznan, Poland (Sliwowska and Ziarniak); and the Horse Genetic Markers Laboratory, Poznan University of Life Sciences, 60-637 Poznan, Poland (Mackowski). Address correspondence to J. Cieslak at the address above, or e-mail: jakub.cieslak@up.poznan.pl. Corresponding Editor: Ernest  Bailey Abstract Only the blue dun coat color, produced by the action of the dun allele on the background of a black base coat, is offcially permitted in the Polish primitive horse (PPH, Konik) breed, yet the population is not visually homogenous and various coat color shades occur. Herein, the molecular background of PPH coat color was studied based on genotyping of known causative variants in equine coat color-related genes (ASIP, MC1R, TBX3, SLC36A1, SLC45A2, PMEL17, and RALY). Additionally, screening for the new polymorphisms was conducted for the ASIP gene coding sequence and the TBX3 1.6-kb insert (associated with the dun dilution). We did not observe the champagne, silver, or cream color dilution variants in the PPH breed. A signifcant association (P < 0.01) was recorded for the genotype in TBX3 gene 1.6 kb in/del and the degree of dun coat dilution, demonstrating that the dominant action of the dun mutation is not fully penetrant. In addition to the effect of the 1.6 kb in/del zygosity, variants within the TBX3 insert were signifcantly associated with PPH coat color variability (P < 0.01), suggesting the presence of an additional allele at this locus. Finally, we identifed a high frequency (35%) of genetically bay dun-colored PPH individuals that are offcially recorded as blue (black base coat) duns. We propose that the diffculty in distinguishing these 2 phenotypes visually is due to an independent locus upstream of the ASIP gene, which was recently described as darkening the typical bay pigmentation shade. Subject Area: Genotype to phenotype Key words: DNA polymorphism, dun coat color shade, equine pigmentation The Polish primitive horse (PPH; also known as Konik) is a local breed originating in eastern Poland. The beginning of organized PPH breeding dates to the 1920s, and the frst volume of the offcial studbook was released in 1962 (Mackowski et al. 2015). The main features of the PPH are a primitive body conformation, adapta- tion to the natural habitat, feed effciency, good general health, and Downloaded from https://academic.oup.com/jhered/article/112/5/436/6357767 by guest on 12 December 2023