A Chromosome-level Genome Assembly of the Western Nose-Horned Viper (Vipera ammodytes ammodytes).

We present a chromosome-level genome assembly of the western nose-horned viper (Vipera ammodytes ammodytes), the most medically important viper in Europe. Using PacBio Sequel and Illumina HiSeq X Ten sequencing, we generated ∼270 Gb of data, achieving ∼131× coverage of the genome. The final assembly spans 1.55 Gb with a contig N50 of 45.9 Mb and a scaffold N50 of 210 Mb, anchored into 18 pseudo-chromosomes. Completeness was supported by recovery of 97.1% of Vertebrata BUSCOs. A total of 20,775 protein-coding genes were predicted, of which 96.6% were functionally annotated. Repetitive sequences accounted for 53.75% of the genome, dominated by LINEs (41.87%) and LTRs (14.35%). We identified 112 venom-related genes across 15 families, with expansions in SVMPs, Snaclecs, sPLA₂s, SPIs, and SVSPs, together comprising 62.5% of the venom repertoire. Chemosensory genes were also expanded, including 448 olfactory receptors, 72 taste receptors, and 29 vomeronasal receptors. This assembly represents the most complete genome resource for a true viper to date and provides a key resource for investigating venom evolution, chemosensory adaptation, and comparative snake genomics.