Comparative analysis of the karyotypes of Equus caballus and Equus asinus in the context of contemporary genomic data.

Karyotypes of species within the genus Equus display considerable variation in chromosome number and are characterised by numerous structural rearrangements that have played a pivotal role in their evolutionary divergence and speciation. Equus caballus (horse), 2n = 64 and Equus asinus (donkey), 2n = 62, constitute particularly interesting models for comparative studies due to the diversified morphology of their chromosomes, including acrocentric and submetacentric pairs, documented Robertsonian translocations, and centric fusions. In recent decades, widely applied molecular cytogenetic techniques, especially fluorescence in situ hybridisation (FISH), have enabled the identification of homologous regions, the determination of breakpoint locations, and the precise mapping of chromosomal fragments. Simultaneously, the rapid development of sequencing technologies has allowed for the generation of complete genomic assemblies and the detection of numerous rearrangements that were not identified by earlier methods. Despite these advances, comprehensive physical validation of the most variable chromosomal regions in both species is still lacking, which limits a full understanding of karyotype dynamics and its evolutionary significance. For this reason, further studies involving systematic BAC probe mapping and the integration of FISH data with advanced genomic techniques are warranted. Such an interdisciplinary framework would facilitate the construction of a high-resolution physical map of the genomes of Equus caballus and Equus asinus, thereby advancing our understanding of the mechanisms underlying speciation within the genus Equus.