Whole-Genome Sequencing Reveals Breed-Specific SNPs, Indels, and Signatures of Selection in Royal White and White Dorper Sheep

Abstract

Whole-genome sequencing (WGS) is a powerful tool for uncovering genome-wide variation, identifying selection signatures, and guiding genetic improvement in livestock. Royal White (RW) and White Dorper (WD) sheep are economically important meat-type hair breeds in the U.S., yet their genomic architecture remains poorly characterized. In this study, WGS was performed on 20 ewes (<i>n</i> = 11 RW, <i>n</i> = 9 WD) to identify and annotate SNPs and small insertions and deletions (indels). Functional annotation, gene enrichment, population structure, and selective sweep analysis were also performed. Selective sweep analysis was conducted by integrating the fixation index (F_ST), nucleotide diversity (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>&pi;</mi></semantics></math></inline-formula>), and Tajima&rsquo;s D to identify candidate regions under putative recent positive selection. A total of 21,957,139 SNPs and 2,866,600 indels were identified in RW sheep, whereas 18,641,789 SNPs and 2,397,368 indels were identified in WD sheep. In RW sheep, candidate genes under selection were associated with health and parasite resistance (<i>NRXN1</i>, <i>HERC6</i>, <i>TGFB2</i>) and growth traits (<i>JADE2</i>). In WD sheep, selective sweep regions included genes linked to immune response and parasite resistance (<i>TRIM14</i>), body weight (<i>PLXDC2</i>), and reproduction (<i>STPG3</i>). These findings were supported by sheep-specific quantitative trait loci (QTL) annotations and previously reported SNP&ndash;trait associations. This study provides the first WGS-based genomic comparison between RW and WD sheep, establishing a foundation for future genetic improvement, including targeted selection for enhanced immune function, disease resistance, and other economically important traits in these breeds.