Complete Telomere-to-Telomere Assembly of the Y Chromosome in the Chinese Quartet

The complete assembly of the human Y chromosome remains a formidable task due to its highly repetitive, palindromic, and heterochromatic architecture. While complete telomere-to-telomere (T2T) assemblies have recently been generated for select individuals, high-quality, gapless Y chromosome references for East Asian lineages--specifically within well-characterized multi-omics reference cohorts--remain scarce. The Chinese Quartet (CQ), comprising monozygotic twin daughters and their parents, represents a premier national reference material system for genomic standardization. However, because the female offspring inherited their father's X chromosome rather than his Y chromosome, previous pedigree-based T2T assemblies (CQ v3.2) lacked a gapless Y chromosome sequence. Here, we present a complete, gapless T2T assembly of the Y chromosome (designated CQ_chrY) from the father of the CQ. This assembly was generated by integrating Oxford Nanopore Technologies ultra-long reads, PacBio high-fidelity reads, and Hi-C data, resulting in a sequence of 68.50 Mb. The assembly shows exceptional base accuracy (QV = 57.54) and structural assembly quality (CRAQ AQI = 99.781). We completely resolved the 40.09 Mb Yq12 heterochromatic region, a ~940 kb centromeric higher-order repeat array, and annotated 96 protein-coding gene models evaluated against GENCODE/T2T-Y standards, alongside 57.59 Mb (84.07%) of repetitive elements. CQ_chrY serves as a complementary paternal resource extending the CQ reference platform, providing a robust foundation for population genetics, structural variation analysis, and East Asian genomic standardization.