Dna chimpanzee vs human1/16/2024 Total genomic DNA from an individual male chimpanzee was mechanically fragmented using a nebulizer. The results reveal complex patterns of accumulation of DNA sequence differences that are distinct with regard both to various classes of substitutions and to different chromosomes. About two thirds could be unambiguously aligned to DNA sequences in humans. To better understand how DNA sequences have changed during recent human evolution, we have determined ∼3 Mb from >10,000 regions in the chimpanzee genome. Therefore, sampling of a large number of DNA sequences is required to gain an overview of the extent and pattern of divergence between the chimpanzee and human genomes. However, different regions of the human genome differ in base composition (Bernardi 1995) and in extent of divergence from the chimpanzee (Dorit et al. Only recently, a study of 53 intergenic autosomal regions in the chimpanzee genome (Chen and Li 2001) indicated that the extent of divergence is only 1.24%. Since that time, little additional knowledge about the pattern of divergence has accumulated. 1991) established that the extent of DNA sequence difference is on the order of 1.6%. Second, because of the short divergence time, processes that may influence the accumulation of DNA sequence changes-for example, regional differences in recombination and mutation rates-can be assumed not to have changed drastically since the two species shared a common ancestor.Įarly comparative studies of the human and chimpanzee genomes (King and Wilson 1975 Sibley and Ahlquist 1984 Goodman et al. First, the close relationship between the sequences compared minimizes the risk that multiple substitutions at the same sites will obscure the results. Thus, for a study of the accumulation of nucleotide substitutions in the human genome, chimpanzees offer the most relevant nonhuman comparison, for at least two reasons. However, since the extent of divergence differs significantly among autosomes, additional unknown factors must also influence the accumulation of substitutions in the human genome.Ĭhimpanzees and humans are estimated to have shared a common ancestor only 4.6–6.2 million years ago (Chen and Li 2001). Thus, the relative time spent in the male and female germlines may be a major determinant of the overall accumulation of nucleotide substitutions. If the nucleotide diversity in the common ancestral species of humans and chimpanzees is assumed to have been about fourfold higher than in contemporary humans, all possible comparisons between autosomes and X and Y chromosomes result in estimates of the ratio between male and female mutation rates of ∼3. Whereas ∼15% of all CpG sites have experienced changes between humans and chimpanzees, owing to a 23-fold excess of transitions and a 7-fold excess of transversions, substitutions at other sites vary in frequency, between 0.1% and 0.5%. Although the average sequence difference is low (1.24%), the extent of changes is markedly different among sites and types of substitutions. A total of 8,859 DNA sequences encompassing ∼1.9 million base pairs of the chimpanzee genome were sequenced and compared to corresponding human DNA sequences.
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