Unveiling the population genetic structure of Iranian horses breeds by whole-genome resequencing analysis

Preserving genetic diversity is pivotal for enhancing genetic improvement and facilitating adaptive responses to selection. This study focuses on identifying key genetic variants, including single nucleotide polymorphisms (SNPs), insertion/deletion polymorphisms (INDELs), and copy number variants (CNVs), while exploring the genomic evolutionary connectedness among seven Iranian horses representing five indigenous breeds: Caspian, Turkemen, DareShuri, Kurdish, and Asil. Using whole-genome resequencing, we generated 2.7 Gb of sequence data, with raw reads ranging from 1.2 Gb for Caspian horses to 0.38 Gb for Turkoman horses. Post-filtering, approximately 1.9 Gb of reads remained, with similar to 1.5 Gb successfully mapped to the horse reference genome (EquCab3.0), achieving mapping rates between 76.4% (Caspian) and 98.35% (Turkoman). We identified 2,909,816 SNPs in Caspian horses, constituting around 0.1% of the genome. Notably, 71% of these SNPs were situated in intergenic regions, while 8.5 and 6.8% were located upstream and downstream, respectively. A comparative analysis of SNPs between Iranian and non-Iranian horse breeds showed that Caspian horses had the lowest number of shared SNPs with Turkoman horses. Instead, they showed a closer genetic relationship with DareShuri, Quarter, Arabian, Standardbred, and Asil breeds. Hierarchical clustering highlighted Caspian horses as a distinct cluster, underscoring their distinctive genomic signature. Caspian horses exhibit a unique genetic profile marked by an enrichment of private mutations in neurological genes, influencing sensory perception and awareness. This distinct genetic makeup shapes mating preferences and signifies a separate evolutionary trajectory. Additionally, significant non-synonymous single nucleotide polymorphisms (nsSNPs) in reproductive genes offer intervention opportunities for managing Caspian horses. These findings reveal the population genetic structure of Iranian horse breeds, contributing to the advancement of knowledge in areas such as conservation, performance traits, climate adaptation, reproduction, and resistance to diseases in equine science.