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Updated: May 25, 2026

Novel Sequence Discovery by Subtractive Genomics
Published on: January 25, 2019
Under-representation of repetitive sequences in whole-genome shotgun sequence databases: an illustration using a
1Division of Genome Diversity, Primate Research Institute, Kyoto University, Inuyama City, Japan. koga@pri.kyoto-u.ac.jp
Abstract:
It is widely accepted in a conceptual framework that repetitive sequences, especially those with high sequence homogeneity among copies, tend to be under-represented in whole-genome shotgun sequence databases, because of the difficulty of assembling sequence reads into contigs. Although this is easily inferred, there is no quantitative illustration of this phenomenon. An example using a currently used database is expected to contribute to the intuitive understanding of how serious the under-representation is. The present study provides the first quantitative example (in the case of 16 copies of virtually identical, 4.7-kb sequences in a genome of 7 × 10 (8) bp) by comparing the results of BLAST searches of a sequence database (contig N50; 9.8 kb) with those of Southern blot analysis of genomic DNA. This has revealed that the internal regions of the repetitive sequences are under-represented to a striking extent.
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