From markers to mechanisms: a comprehensive review of major genes and quantitative trait loci shaping the modern sheep (Ovis aries)
One of the most important agricultural industries in the world is sheep ( Ovis aries ), considering essential resources such as meat, milk, and wool. Genetic and genomics innovations have significantly improved the efficiency and sustainability of sheep production, which requires a thorough knowledge of the genetic basis of economically relevant traits that are controlled. This is a comprehensive review of the historical development of sheep genetics, from basic stages in the use of microsatellite markers in linkage mapping to the current environment of high-throughput genotyping methods, whole-genome sequencing, and GS (Genomic Selection), which collectively form the basis of contemporary improvement programs. The review is organized by major trait categories, which include growth and body composition, reproduction and fertility, wool quality, and disease resistance. The major genes and QTL (Quantitative trait loci) of each category are defined and described, as well as their biological roles, molecular mechanisms, and their usage in modern breeding solutions are discussed. The most important methodologies that enable these discoveries are elucidated, including linkage analysis, GWAS (Genome-wide association studies), RNA-sequencing (RNA-Seq), and newly emerging multi-omics approaches. Comparative studies also show that there are conserved genetic processes and structures in various sheep breeds and other livestock species, specifically cattle, which indicates species-specific and common regulatory pathways. Rather than claiming to be an exhaustive historical record, this narrative review synthesizes major advances in sheep genetic mapping, functional genomics, and GS relevant to economically important traits. By critically evaluating the strength of evidence, mapping resolution, and practical breeding applications, this work aims to provide researchers, breeders, and students with a balanced, evidence-based resource to guide future genomic improvements in sustainable sheep production.