Search

Advances in high-throughput genotyping technologies have afforded researchers the opportunity to study ever-increasing numbers of SNP in animal genomes. However, many studies encounter difficulties in obtaining sufficient quantities of high-quality DNA for such analyses, particularly when the source biological material is limited or degraded. The recent development of in vitro whole-genome amplification approaches has permitted researchers to circumvent these challenges by increasing the amount of usable DNA in normally small-quantity samples. Here, we assess the performance of whole-genome amplification products generated from ovine genomic DNA using a high-throughput SNP genotyping platform, the newly developed Illumina ovineSNP50 BeadChip. Our results demonstrate a high genotype call rate for conventional genomic DNA and whole-genome amplified genomic DNA. The data also reveal an exceptionally high concordance rate ([greater than or equal to] 99%) between the genotypes generated from whole-genome amplified products and their conventional genomic DNA counterparts. This study supports the use of whole-genome amplification as a viable solution for the analysis of high-density SNP genotypic data using compromised or limited starting material. Key words: BeadChip array, genotyping, Ovis aries, sheep, single nucleotide polymorphism, whole-genome amplified DNA doi: 10.2527/jas.2009-2723

Genotypes at the retinoic acid receptor-related orphan receptor C (RORC) gene were associated with fatness in 1750 cattle. Ten SNPs were genotyped in RORC and the adjacent gene leucine-rich repeat neuronal 6D (LRRN6D) to map the QTL, 7 of which are in a 4.2-kb sequence around the ligand-binding domain of the RORC gene. Of the 29 inferred haplotypes for these SNPs, 2 have a combined frequency of 54.6% while the top 5 haplotypes have a combined frequency of 85.3%. The average D' value of linkage disequilibrium was 0.92 although the average [r.sup.2] was a low 0.18. The RORC:g.3290T>G SNP had the strongest association with marbling. The inferred haplotypes were significantly associated with marbling and the difference between the most divergent haplotypes was 0.35 [[sigma].sub.p] of marbling and 0.28 [[sigma].sub.P] of rump fat, explaining the previously reported QTL effect, cDNA for RORC were sequenced and 2 new alternative transcripts were found. Fetal tissue shows 40 times greater transcription of RORC than adult tissue. The highest expression in fetal tissue was found in liver and kidney, but in adults the longissimus muscle had the greatest expression of the tissues tested.

Research on European and Asian sheep breeds shows that sheep possess the highest intercontinental dispersal rate and the weakest population structure of all domestic animals to date. Introgression was found to have had a key role in breeding development and also in subsequent selection.

Most published genomewide association studies ( GWAS) in sheep have investigated recessively inherited monogenic traits. The objective here was to assess the feasibility of performing GWAS for a dominant trait for which the genetic basis was already known. A total of 42 Manchega and Rasa Aragonesa sheep that segregate solid black or white coat pigmentation were genotyped using the SNP50 Bead Chip. Previous analysis in Manchegas demonstrated a complete association between the pigmentation trait and alleles of the MC1R gene, setting an a priori expectation for GWAS. Multiple methods were used to identify and quantify the strength of population substructure between black and white animals, before allelic association testing was performed for 49 034 SNPs. Following correction for substructure, GWAS identified the most strongly associated SNP ( s26449) was also the closest to the MC1 R gene. The finding was strongly supported by the permutation tree-based random forest ( RF) analysis. Importantly, GWAS identified unlinked SNP with only slightly lower p-values than for s26449. Random forest analysis indicated these were false positives, suggesting interpretation based on both approaches was beneficial. The results indicate that a combined analytical approach can be successful in studies where a modest number of animals are available and substantial population stratification exists. [ABSTRACT FROM AUTHOR]