Abstract
BackgroundNative Swedish sheep breeds are part of the North European short-tailed sheep group; characterized in part by their genetic uniqueness. Our objective was to study the population structure of native Swedish sheep. Five breeds were genotyped using the 600 K SNP array. Dalapäls and Klövsjö sheep are from the middle of Sweden; Gotland and Gute sheep from Gotland, an island in the Baltic Sea; and Fjällnäs sheep from northern Sweden. We studied population structure by: principal component analysis (PCA), cluster-based analysis of admixture, and an estimated population tree.ResultsThe analyses of the five Swedish breeds revealed that these breeds are five distinct breeds, while Gute and Gotland are more closely related to each other as seen in all analyses. All breeds had long branch lengths in the population tree indicating they’ve been subjected to drift. We repeated our analyses using 39 K SNP and including 50 K SNP genotypes from other European and southwestern Asian breeds from the Sheep HapMap project and 600 K SNP genotypes from a dataset of French sheep. Results arranged breeds into five groups: south-west Asia, south-west Europe, central Europe, north Europe and north European short-tailed sheep. Within this last group, Norwegian and Icelandic breeds, Finn and Romanov sheep, Scottish breeds, and Gute and Gotland sheep were more closely related while the remaining Swedish breeds and Ouessant sheep were distinct from all breeds and had longer branches in the population tree.ConclusionsWe showed population structure of five Swedish breeds and their structure within European and southwestern Asian breeds. Swedish breeds are unique, distinct breeds that have been subjected to drift but group with other north European short-tailed sheep.
Highlights
Native Swedish sheep breeds are part of the North European short-tailed sheep group; characterized in part by their genetic uniqueness
Genetic diversity has only been studied in some of these breeds: microsatellite markers were used for comparing north European short-tailed sheep [4] and northern Eurasian breeds [5]; population history has been studied in native Swedish breeds using endogenous retroviruses to compare genotypes with Texel and British breeds [6, 7]; and seven microsatellite markers and pedigree data were used to estimate inbreeding and genetic diversity in a local Swedish breed, Gute sheep [8]
All genetic diversity measures estimated for the five native Swedish sheep breeds are in Table 1 including three inbreeding measures and expected and observed heterozygosity
Summary
Native Swedish sheep breeds are part of the North European short-tailed sheep group; characterized in part by their genetic uniqueness. Some north European short tailed sheep breeds were included in the Sheep HapMap project [9] where many breeds from around the world were genotyped using a medium-density SNP array [10]. Native Swedish breeds have not yet been genotyped at medium- or high-density and have not been included in comparisons with breeds from around the world and were not part of the Sheep HapMap project. These comparisons and studies using a higher density of DNA markers will be important for informing future discussions on the conservation of these breeds
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