Genome-wide population structure and admixture analysis reveals weak differentiation among Ugandan goat breeds

Summary

Uganda is endowed with a large population of goats from predominantly indigenous breeds reared in diverse production systems, whose existence is threatened by crossbreeding with exotic Boer goats. Knowledge about the genetic characteristics and relationships among these Ugandan goat breeds and the potential admixture of the exotic breed Boer is still limited. Using a medium density single nucleotide polymorphism (SNP) panel, we assessed the genetic diversity, population structure and admixture in six Ugandan goat breeds. Samples from five indigenous Ugandan goat breeds including Mubende (n=29), Kigezi (n=29), Small East African (n=29), Sebei (n=29) and Karamojong (n=15), and the exotic breed Boer (n=13) from different agro-ecological regions of Uganda were genotyped using the GoatSNP50 BeadChip. Analysis of genotype data revealed high levels of polymorphism with the proportion of polymorphic SNPs ranging from 0.885 in Kigezi to 0.928 in Sebei. The overall mean genetic diversity indices across breeds for HO and HE was 0.355±0.147 and 0.384±0.143 respectively. Principle components, genetic distances and ADMIXTURE analyses revealed weak population sub-structuring among the breeds. Principle components separate Kigezi and weakly Small East African from other indigenous goats. Sebei and Karamojong are tightly entangled together while Mubende occupies a more central position with high admixture from all other local breeds. The Boer breed showed a unique cluster from the Ugandan indigenous goat breeds. The results reflect common ancestry but also some level of geographical differentiation. ADMIXTURE and four population test analyses further revealed gene-flow from Boer to Ugandan indigenous goat breeds and varying levels of admixture among the Ugandan indigenous breeds. Generally, moderate to high levels of genetic variability were observed in the Ugandan goat breeds. Our findings provide useful insight to devise strategies to maintain genetic diversity in local goat breeds from Uganda and to design appropriate breeding programs to exploit within breed diversity and heterozygote advantage in cross-breeding schemes.