Analysis of tandem repeats in seven telomere-to-telomere primate genomes.

Tandem repeats (TRs) are highly polymorphic low complexity regions present in all the genomes. The length variation in TRs, particularly that of short TRs (STRs), is associated with several cellular functions such as gene expression and genome organization. In humans, an abnormal expansion of a few STR loci is linked to neurodegenerative diseases. Despite their importance, limitations and gaps in reference genomes prohibit the comprehensive analysis of TRs. Recent advances in high-throughput sequencing technologies have enabled the generation of gapless, telomere-to-telomere (T2T) genomes of humans and other ape species. Here, we report the TR landscape of seven primate T2T genomes, including humans. Our analysis indicates that TRs of 1-100 nucleotide (nt) motifs cover 3.5-6.9% of large primate genomes, with the highest density observed in gorilla (69 kb per Mbp). Large motif size TRs are prevalent and contribute abundantly to higher-order repeats. As an example, we describe a species-specific 32 nt A/T rich motif that contributes to subtelomeric repeats. Finally, we present the motif decomposition and substructure of pentameric repeats in Y chromosomes of six ape species. Our work illutrates the dynamics of TRs in large genomes, and showcases the utility of complete genomes for better understanding the role of low complexity sequences.