Genome-wide selection signatures in Turkish Awassi sheep: uncovering the genetic basis of production traits and adaptation

The Awassi sheep is one of the leading fat-tailed breeds of the Fertile Crescent, known for its high milk yield and resilience in arid and semi-arid environments. Despite its socio-economic importance, a high-resolution genomic characterization of selection signatures in Turkish Awassi populations remains limited. This study aimed to investigate the genomic diversity, demographic history, and selection signatures of Turkish Awassi sheep using double-digest restriction-site-associated DNA sequencing (ddRADseq). Genome-wide single-nucleotide polymorphism (SNP) discovery was performed on 40 unrelated Awassi sheep. Genetic diversity parameters, historical effective population size ( N _e ), and linkage disequilibrium (LD) decay were assessed. Selection signatures were identified using both runs of homozygosity (ROH) islands and Tajima's D analyses, followed by functional annotation of candidate genes. A total of 397 315 high-quality SNPs were identified. The average minor allele frequency (MAF) was 0.333, and the ROH-based inbreeding coefficient ( F _ROH ) was low (0.025), indicating high genetic integrity. The historical N _e showed a consistent decline, reaching 147 in the most recent generations. Selection signature analysis identified 21 and 48 protein-coding genes by means of ROH and Tajima's D , respectively. The key candidate genes were associated with milk yield and lactation ( AKR1C3 , AKR1D1 , OXT , AVP , ZNF131 ), meat production and growth ( PBX1 , KBTBD8 , HOXA cluster, ADGB ), fat-tail formation ( HOXA cluster, HMGCS1 , STARD4 ), and environmental adaptation ( ABCB1 , TSLP , IL6 ). Our findings reveal that the Turkish Awassi genome is a rich genetic reservoir shaped by combined natural and artificial selection. The selection signatures identified in this study provide fundamental genomic targets for future breeding strategies to enhance productivity without compromising environmental resilience. These findings support the use of Turkish Awassi as a genetic resource for breeding programs in arid and semi-arid production systems.