Genetic aspects of polledness in sheep (review)

The analysis of the genetic mechanisms underlying the presence or absence of horns is of interest both for understanding evolutionary processes and for realizing the economic benefits of breeding polled animals. The creation of polled sheep breeds has become an important breeding goal in many countries with developed sheep breeding industries, as these breeds are more technologically efficient to manage and require less feed. Mapping genetic variability to specific candidate loci allows the most accurate assessment of the influence of individual alleles and the genotype-phenotype relationship of hornedness and polledness. This review analyzes the current state of research aimed at identifying genes and genomic regions associated with polledness in sheep, and explores the potential of using genomic approaches in breeding programs for polled breeds. The inheritance of polledness is complex, as its expression differs between sexes, and no single-locus model with complete penetrance can fully explain the observed phenotypic variability within and between breeds. The RXFP2 (relaxin/insulin-like family peptide receptor 2) marker gene is shown to be promising for further study in different breeds for use in breeding programmes. Genome editing and transcriptome analysis are promising approaches to fully understand the mechanism by which different *RXFP2* alleles influence horn morphology and to develop polled animals. Accumulating knowledge in this area will enable a more complete understanding of the genetic mechanisms underlying the polled phenotype in sheep.