The authors compared the conservation of DNA sequences making up the bulk of gene-regulating elements and found marked conservation in the regulatory regions between mice and rats, but nearly none between humans and chimps. This result suggests that the gene-regulating elements of hominids are subject to nearly unfettered mutation accumulation. Keightley and colleagues propose that selection is ineffective against mildly unfavorable mutations in the gene-regulating regions of hominids because of the small effective population size in their evolutionary history.
What do these results suggest for the future of human evolution? It's unlikely that the regulatory gatekeepers of our genome will allow mutations to spin out of control. Even if the number of unwanted mutations were to increase, stronger natural selection against them is likely to develop in parallel, Keightley and colleagues explain, protecting our fitness from a downward spiral. The authors' results, however, support the notion that population size exerts a powerful influence on evolutionary changes at the molecular level. With each new sequenced genome added to the comparative genomics lexicon, scientists are becoming increasingly conversant in the grammar and syntax of gene sequences--and filling in more and more gaps in the human story, letter by letter.
Citation: Keightley PD, Lercher MJ, Eyre-Walker A (2005) Evidence for widespread degradation of gene control regions in hominid genomes. PLoS Biol 3 (2): e42.
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