Wool: From Properties and Structure to Genetic Insights and Sheep Improvement Strategies

The wool of sheep consists of structurally intricate natural fibres that can be processed and manufactured into a range of products. It is prized for its insulation, moisture-buffering capability, flame resistance, and biodegradability. These features arise from its unique fibre architecture and specialised protein composition, which set it apart from most other natural and synthetic fibres. However, despite these novel characteristics, wool fibre variation hampers its uses and reduces its ability to compete with other fibres. This review summarises our current knowledge of wool fibre biology. It begins with a description of wool’s functional properties and performance attributes, then explores the structural foundations of these properties, the molecular basis of fibre trait variation, and prospects for improving fibre quality using genetic approaches. Particular attention is given to the wool keratin and keratin-associated protein genes, their spatiotemporal expression patterns, and genetic polymorphism that may influence fibre characteristics. Opportunities for the genetic improvement of sheep are discussed, including the use of genetic modification and marker-assisted selection. Challenges in interpreting gene–trait associations, particularly from high-throughput omics studies, are highlighted, along with the need for functionally validated genetic markers. Potential trade-offs between wool characteristics and other production and reproductive traits are considered, emphasising the need for balanced breeding approaches. By integrating insights from structural biology, molecular genetics, and breeding strategies, this review provides a foundation for wool fibre improvement.