Data from: Merino and Merino-derived sheep breeds: a genome-wide intercontinental study

Background: Merino and Merino-derived sheep breeds have been widely
distributed across the world, both as purebred and admixed populations.
They represent an economically and historically important genetic resource
which over time has been used as the basis for the development of new
breeds. In order to examine the genetic influence of Merino in the context
of a global collection of domestic sheep breeds, we analyzed genotype data
that were obtained with the OvineSNP50 BeadChip (Illumina) for 671
individuals from 37 populations, including a subset of breeds from the
Sheep HapMap dataset. Results: Based on a multi-dimensional scaling
analysis, we highlighted four main clusters in this dataset, which
corresponded to wild sheep, mouflon, primitive North European breeds and
modern sheep (including Merino), respectively. The neighbor-network
analysis further differentiated North-European and Mediterranean domestic
breeds, with subclusters of Merino and Merino-derived breeds, other
Spanish breeds and other Italian breeds. Model-based clustering, migration
analysis and haplotype sharing indicated that genetic exchange occurred
between archaic populations and also that a more recent Merino-mediated
gene flow to several Merino-derived populations around the world took
place. The close relationship between Spanish Merino and other Spanish
breeds was consistent with an Iberian origin for the Merino breed, with
possible earlier contributions from other Mediterranean stocks. The Merino
populations from Australia, New Zealand and China were clearly separated
from their European ancestors. We observed a genetic substructuring in the
Spanish Merino population, which reflects recent herd management
practices. Conclusions: Our data suggest that intensive gene flow, founder
effects and geographic isolation are the main factors that determined the
genetic makeup of current Merino and Merino-derived breeds. To explain how
the current Merino and Merino-derived breeds were obtained, we propose a
scenario that includes several consecutive migrations of sheep populations
that may serve as working hypotheses for subsequent studies.