The T2T-CHM13v2.0 reference genome added previously uncharacterized genomic sequences and improved the accuracy of repetitive stretches compared to former human genome assemblies. By comprehensive allelic variation analysis and read mapping statistics from sequencing reads aligned to hg38 and T2T-CHM13 assemblies in samples encompassing different sequencing designs and ethnicity groups, we observed that T2T-CHM13v2.0 assembly significantly reduces the reference mapping bias (RMB) and increases read mapping precision at clinically relevant sites, including BRCA1 pathogenic variants. Further, we report the presence of sequence dissimilarities among reference genomes in the proximity of ClinVar annotated variants, suggesting the need for data re-analysis and potential redesign of probes targeting clinically relevant regions. Overall, these findings support the implementation of T2T-CHM13 reference for the improvement of sequencing data analyses in the clinical genomic setting. ### Competing Interest Statement The authors have declared no competing interest. Fondazione AIRC per la ricerca sul cancro, IT, 22792 Fondazione Cassa Di Risparmio Di Trento E Rovereto, IT Cancer Research UK, https://ror.org/054225q67, A26822 Department of CIBIO – University of Trento

In the 150 years since chromosomes were first discovered, scientists have studied them in various contexts, from insect cells to artificial systems.