RESUMEN
Genetic architecture of sheep reproduction is increasingly gaining scientific interest due to the major impact on sheep production systems. In the present study, we conducted pedigree-based analyses and genome-wide association studies using the Illumina Ovine SNP50K BeadChip to explore the genetic mechanisms underlying the reproduction of the highly prolific Chios dairy sheep. First lambing age, total prolificacy and maternal lamb survival were selected as representative reproductive traits and estimated as significantly heritable (h2â¯=â¯0.07-0.21) with no evident genetic antagonism among traits. We identified novel genome-wide and suggestive significant single-nucleotide polymorphisms (SNPs) on chromosomes 2 and 12 associated with age at first lambing. The new variants detected on chromosome 2 span a region of 357.79â¯kb with high pairwise linkage disequilibrium estimates (r2â¯=â¯0.8-0.9). Functional annotation analysis revealed candidate genes, such as the collagen-type genes and the Myostatin gene, that participate in osteogenesis, myogenesis, skeletal and muscle mass development resembling the functionality of major genes affecting the ovulation rate and prolificacy. Additional functional enrichment analysis associated the collagen-type genes with multiple uterine-related disfunctions, such as cervical insufficiency, uterine prolapse and abnormalities of the uterine cervix. Several genes (e.g., KAZN, PRDM2, PDPN, LRRC28) localised close to the SNP marker on chromosome 12 were grouped in annotation enrichment clusters majorly involved in developmental and biosynthetic pathways, apoptosis, and nucleic acid-templated transcription. Our findings may further contribute to unravel the genomic regions that are important for sheep reproduction and could be incorporated into future selective breeding programmes.
Asunto(s)
Estudio de Asociación del Genoma Completo , Reproducción , Femenino , Ovinos/genética , Animales , Estudio de Asociación del Genoma Completo/veterinaria , Reproducción/genética , Genoma , Fenotipo , Genómica , Polimorfismo de Nucleótido Simple , Colágeno/genéticaRESUMEN
Caseins are widely used for species identification of dairy products. Isoelectric focusing (IEF) of para-κ-casein peptide is used as the official German method for the differentiation between caprine (isoform A) and ovine (isoform B) dairy products, based on their different isoelectric points. The discrimination between Greek goat and ewe dairy products using IEF has, however, been shown to be problematic because of the existence of the ewe isoform in milk from Greek indigenous dairy goats. This could be due to nucleotide polymorphisms within the goat κ-casein gene of Greek indigenous breeds, which alter the isoelectric point of the para-κ-casein peptide and lead to false positive results. Previous DNA analysis of the goat κ-casein gene has shown high levels of polymorphism; however, no such information is available for Greek indigenous dairy goats. Therefore, 87 indigenous dairy goats were sequenced at exon IV of κ-casein gene. In total, 9 polymorphic sites were detected. Three nonsynonymous point mutations were identified, which change the isoelectric point of the goat para-κ-casein peptide so that it appears identical to that of the ewe peptide. Ten composite genotypes were reconstructed and 6 of them included the problematic point mutations. For the verification of genetic results, IEF was carried out. Both goat and ewe patterns appeared in the problematic genotypes. The frequency of these genotypes could be characterized as moderate (0.23) to high (0.60) within Greek indigenous breeds. However, this is not an issue restricted to Greece, as such genotypes have been detected in various non-Greek goat breeds. In conclusion, IEF based on the official German method is certainly inappropriate for ovine and caprine discrimination concerning Greek dairy goat products, and consequently a new method should be established.