Differentiation among Spanish sheep breeds using microsatellites

Genetic variability at 18 microsatellites was analysed on the basis of indi vidual genotypes in five Spanish breeds of sheep-Churra, Latxa, Castellana, Rasa-Aragonesa and Merino-, with Awassi also being studied as a reference breed. The degree of population subdivision calculated between Spanish bree ds from F-ST diversity indices was around 7% of total variability. A high d egree of reliability was obtained for individual-breed assignment from the 18 loci by using different approaches among which the Bayesian method provi ded to be the most efficient, with an accuracy for nine microsatellites of over 99%. Analysis of the Bayesian assignment criterion illustrated the div ergence between any one breed and the others, which was highest for Awassi sheep, while no great differences were evident among the Spanish breeds. Re lationships between individuals were analysed from the proportion of shared alleles. The resulting dendrogram showed a remarkable breed structure, wit h the highest level of clustering among members of the Spanish breeds in La txa and the lowest in Merino sheep, the latter breed exhibiting a peculiar pattern of clustering, with animals grouped into several closely set nodes. Analysis of individual genotypes provided valuable information for underst anding intra- and inter-population genetic differences and allowed for a di scussion with previously reported results using populations as taxonomic un its.