Comparative Genomic Analysis of Human and Chimpanzee Indicates a Key Role for Indels in Primate Evolution
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Sequence comparison of humans and chimpanzees is of interest to understand the mechanisms behind primate evolution. Here we present an independent analysis of human chromosome 21 and the high-quality BAC clone sequences of the homologous chimpanzee chromosome 22. In contrast to previous studies, we have used global alignment methods and Ensembl predictions of protein coding genes (n = 224) for the analysis. Divergence due to insertions and deletions (indels) along with substitutions was examined separately for different genomic features (coding, noncoding genic, and intergenic sequence). The major part of the genomic divergence could be attributed to indels (5.07%), while the nucleotide divergence was estimated as 1.52%. Thus the total divergence was estimated as 6.58%. When excluding repeats and low-complexity DNA the total divergence decreased to 2.37%. The chromosomal distribution of nucleotide substitutions and indel events was significantly correlated. To further examine the role of indels in primate evolution we focused on coding sequences. Indels were found within the coding sequence of 13% of the genes and approximately half of the indels have not been reported previously. In 5% of the chimpanzee genes, indels or substitutions caused premature stop codons that rendered the affected transcripts nonfunctional. Taken together, our findings demonstrate that indels comprise the majority of the genomic divergence. Furthermore, indels occur frequently in coding sequences. Our results thereby support the hypothesis that indels may have a key role in primate evolution.
KeywordsIndels Comparative genomics Chimpanzee Primate evolution
We wish to thank The International Chimpanzee Chromosome 22 Consortium for providing the chimpanzee BAC sequences, Ronald Bontrop for providing chimpanzee cell lines, and Bengt-Olle Röken for providing the gorilla sample. We would also like to thank Ulf Gyllensten for valuable comments on the manuscript and Charlotte Johansson for excellent technical assistance. This work was supported by grants from the Graduate Research School in Genomics and Bioinformatics, the Swedish Research Council, the Erik Philip-Sörensen Foundation, the Beijer Foundation, the Marcus Borgström Foundation, and the Magnus Bergvalls Foundation.
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