JG2: an updated version of the Japanese population-specific reference genome

Here we present the construction of JG2, an updated population-specific reference genome for the Japanese population. Utilizing data from three individuals previously used in the construction of JG1, several methodologies were employed to enhance genomic coverage and assembly quality. Hi-C sequencing technology facilitated phase-aware assembly, generating two haploid assemblies per individual and enabling improved representation of genetic variation. A meta-assembly strategy and a majority decision approach further refined assembly quality by combining the best sequences from multiple assemblies and minimizing the inclusion of rare variants. The resulting JG2 genome comprises chromosome-level sequences, mitochondrial chromosomes and unplaced scaffolds, offering more comprehensive coverage of the Japanese genome. Comparative analyses with other reference genomes demonstrated the accuracy and representativeness of JG2, highlighting its utility for genetic research involving the Japanese population. Overall, by adopting the phased assembly technique, JG2 represents a substantial advancement over the collapsed assembly-based JG1, with improvements including a greater number of identified variants (3,115,695 variants, of which 298,644 had an allele frequency (AF) of 1.0 in the 3.5KJPNv2 AF panel) and a higher N50 value (152,668,378 bp). These enhancements provide researchers with a more precise and comprehensive resource for understanding the genetic landscape of the Japanese population. The sequences and annotations are available on the jMorp website ( https://jmorp.megabank.tohoku.ac.jp/ ).