Chimpanzees
From EvoWiki
The word chimpanzee is used for the genus Pan as well as one of the species in the genus. Pan, an African Great ape, the closest living relative of Homo sapiens.
- Pan troglodytes, the chimpanzee.
- Pan paniscus, the bonobo or pygmy chimpanzee.
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Evolution
Humans and chimpanzees diverged around 7 million years ago, and their nucleotide sequences are 0.9-1.31% polymorphic. This relatively recent divergence and low polymorphism has led some scientists to state that chimpanzees and humans belong in the same genus.
Chimpanzee Genome
The first draft of the chimpanzee genome was published in 2005. The key findings of the paper include:
- Single-nucleotide substitutions occur at a mean rate of 1.23% between copies of the human and chimpanzee genome, with 1.06% or less corresponding to fixed divergence between the species.
- Regional variation in nucleotide substitution rates is conserved between the hominid and murid genomes, but rates in subtelomeric regions are disproportionately elevated in the hominids.
- Substitutions at CpG dinucleotides, which constitute one-quarter of all observed substitutions, occur at more similar rates in male and female germ lines than non-CpG substitutions.
- Insertion and deletion (indel) events are fewer in number than single-nucleotide substitutions, but result in ,1.5% of the euchromatic sequence in each species being lineage-specific.
- There are notable differences in the rate of transposable element insertions: short interspersed elements (SINEs) have been threefold more active in humans, whereas chimpanzees have acquired two new families of retroviral elements.
- Orthologous proteins in human and chimpanzee are extremely similar, with ,29% being identical and the typical orthologue differing by only two amino acids, one per lineage.
- The normalized rates of amino-acid-altering substitutions in the hominid lineages are elevated relative to the murid lineages, but close to that seen for common human polymorphisms, implying that positive selection during hominid evolution accounts for a smaller fraction of protein divergence than suggested in some previous reports.
- The substitution rate at silent sites in exons is lower than the rate at nearby intronic sites, consistent with weak purifying selection on silent sites in mammals.
- Analysis of the pattern of human diversity relative to hominid divergence identifies several loci as potential candidates for strong selective sweeps in recent human history.
Chimpanzees and AIDS
AIDS, or the aquired immunodeficiency syndrome, is a zoonotic disease that was transferred to humans through chimpanzees. Humans can carry HIV (Human immunodeficiency virus), while chimpanzees and other primates carry SIV (simian immunodeficiency viruses which are species-specific). While some researchers contend that HIV was spread to humans through a polio vaccine produced in the kidneys of african green monkeys, phylogenetic analysis of HIV and SIV strains has shown that the AIDS virus originated from chimpanzees multiple times, probably through the bushmeat trade, the hunting of primate species for meat.
References
Chen, F. and W. Li. 2001. Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees. American Journal of Human Genetics. 68(2): 444-456.
Rambaut, A. et. al. 2001. Human immunodeficiency virus: Phylogeny and the origin of HIV-1. Nature 410:1047-1048. (full-text, html)
Wildman, D. E. et. al. 2003. Implications of Natural Selection in Shaping 99.4% Nonsynonymous DNA Identity between Humans and Chimpanzees: Enlarging Genus Homo. Proceedings of the National Academy of Sciences 100: 7181-88.
The Chimpanzee Sequencing and Analysis Consortium. Initial sequence of the chimpanzee genome and comparison with the human genome. Nature 437, 69–87 (1 September 2005) doi:10.1038/nature04072. http://www.nature.com/doifinder/10.1038/nature04072
S McBrearty and N G Jablonski. First fossil chimpanzee. Nature 437, 104–108 (1 September 2005) doi:10.1038/nature04008. http://www.nature.com/doifinder/10.1038/nature04008
Nature web focus: the chimpanzee genome http://www.nature.com/nature/focus/chimpgenome/index.html
