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Sheep Populations (sheep + population)
Selected AbstractsThe use of marker-based relationship information to estimate the heritability of body weight in a natural population: a cautionary taleJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2002S. C. Thomas A number of procedures have been developed that allow the genetic parameters of natural populations to be estimated using relationship information inferred from marker data rather than known pedigrees. Three published approaches are available; the regression, pair-wise likelihood and Markov Chain Monte Carlo (MCMC) sib-ship reconstruction methods. These were applied to body weight and molecular data collected from the Soay sheep population of St. Kilda, which has a previously determined pedigree. The regression and pair-wise likelihood approaches do not specify an exact pedigree and yielded unreliable heritability estimates, that were sensitive to alteration of the fixed effects. The MCMC method, which specifies a pedigree prior to heritability estimation, yielded results closer to those determined using the known pedigree. In populations of low average relationship, such as the Soay sheep population, determination of a reliable pedigree is more useful than indirect approaches that do not specify a pedigree. [source] Fine mapping of the FecL locus influencing prolificacy in Lacaune sheepANIMAL GENETICS, Issue 6 2009L. Drouilhet Summary In the Lacaune sheep population, two major loci influencing ovulation rate are segregating: FecX and FecL. The FecXL mutation is a non-conservative substitution (p.Cys53Tyr) in BMP15 that prevents the processing of the protein. Using a statistical approach, FecL has been shown to be an autosomal major gene. A full genome scan localized the FecL locus on sheep chromosome 11. Fine mapping reduced the interval containing FecL to markers BM17132 and FAM117A, corresponding to a synteny block of 1.1 megabases on human chromosome 17, which encompasses 20 genes. The expression of 16 genes from this interval was observed in tissues of the reproductive axis, but expression was not affected in homozygous FecLL females. In this interval, a unique haplotype was associated with the FecLL mutation. This particular haplotype could be predicted by the DLX3:c.*803A>G SNP in the 3, UTR sequence of the DLX3 gene. This SNP provided accurate classification of animals (99.5%) as carriers or non-carriers of the mutation and therefore maybe useful in marker assisted selection. A synergistic action of FecLL and FecXL mutations on both ovulation rate and litter size was demonstrated. Until now, all the Fec genes identified in sheep belong to the bone morphogenetic protein (BMP) system. Based on the human orthologous region, none of the 20 genes in the FecL region corresponds to known molecules in the BMP system. The identification of the FecLL mutation could lead to the discovery of a new pathway involved in the regulation of ovulation rate. [source] Quantitative trait loci underlying milk production traits in sheepANIMAL GENETICS, Issue 4 2009B. Gutiérrez-Gil Summary Improvement of milk production traits in dairy sheep is required to increase the competitiveness of the industry and to maintain the production of high quality cheese in regions of Mediterranean countries with less favourable conditions. Additional improvement over classical selection could be reached if genes with significant effects on the relevant traits were specifically targeted by selection. However, so far, few studies have been undertaken to detect quantitative trait loci (QTL) in dairy sheep. In this study, we present a complete genome scan performed in a commercial population of Spanish Churra sheep to identify chromosomal regions associated with phenotypic variation observed in milk production traits. Eleven half-sib families, including a total of 1213 ewes, were analysed following a daughter design. Genome-wise multi-marker regression analysis revealed a genome-wise significant QTL for milk protein percentage on chromosome 3. Eight other regions, localized on chromosomes 1, 2, 20, 23 and 25, showed suggestive significant linkage associations with some of the analysed traits. To our knowledge, this study represents the first complete genome scan for milk production traits reported in dairy sheep. The experiment described here shows that analysis of commercial dairy sheep populations has the potential to increase our understanding of the genetic determinants of complex production-related traits. [source] Population structure, genetic variation and morphological diversity in indigenous sheep of EthiopiaANIMAL GENETICS, Issue 6 2007S. Gizaw Summary We investigated genetic and morphological diversity and population structure of 14 traditional sheep populations originating from four ecological zones in Ethiopia (sub-alpine, wet highland, sub-humid lowland and arid lowland). All animals (n = 672) were genotyped for 17 microsatellite markers and scored for 12 morphological characters. The sheep were initially classified as fat-tailed (11 populations), thin-tailed (one population) and fat-rumped sheep (two populations). These classifications are thought to correspond to three consecutive introduction events of sheep from the Near-East into East Africa. For the 14 populations, allelic richness ranged from 5.87 to 7.51 and expected heterozygosity (HE) from 0.66 to 0.75. Genetic differentiations (FST values) between all pairs of populations, except between sub-alpine populations, were significantly different from zero (P < 0.001). Cluster analysis of morphological characters and a dendrogram constructed from genetic distances were broadly consistent with the classification into fat-tailed, thin-tailed and fat-rumped sheep. Bayesian cluster analysis using microsatellite markers indicated that there has been further genetic differentiation after the initial introduction of sheep into Ethiopia. Investigation of factors associated with genetic variation showed that an isolation-by-distance model, independently of other factors, explained most of the observed genetic variation. We also obtained a strong indication of adaptive divergence in morphological characters, patterns of morphological variation being highly associated with ecology even when the effect of neutral genetic divergence (FST) was parcelled out in partial Mantel tests. Using a combination of FST values, Bayesian clustering analysis and morphological divergence, we propose a classification of Ethiopian sheep into six breed groups and nine breeds. [source] Sheep genetic diversity in Bhutan using microsatellite markersANIMAL SCIENCE JOURNAL, Issue 2 2010Tashi DORJI ABSTRACT Genotype data from eight microsatellite markers were used to assess genetic diversity and relationships among five indigenous Bhutanese sheep populations, Sakten, Jakar, Sarpang, Sipsu and Tsirang. Estimates of mean observed and expected heterozygosities, mean number of alleles per locus/population were obtained. The highest observed heterozygosities were found in Jakar (0.657) and Sakten (0.647), while the lowest one was found in Tsirang (0.539). Genetic distances, pairwise proportion of different alleles, UPGMA tree, and principal component analysis indicate close relationship among Tsirang, Sipsu and Sarpang populations, while Jakar and Sakten populations are located in one cluster. These two clusters are separated geographically, and show distinct phenotypic as well as molecular characters. We therefore recommend that the Bhutanese native sheep populations be classified into at least two distinct breeds, Jakar-Sakten sheep and Sipsu sheep. Since Jakar and Sakten sheep have different morphological phenotypes, further analyses will be required to understand the genetic differences between these two sheep populations. [source] | ||||||||||