BrainEvolutionandUniquenessintheHumanGenome..doc

Brain Evolution and Uniqueness in the Human Genome Despite an ever-expanding database of sequenced mammalian genomes to be mined for clues, the emergence发生 of the unique human brain remains an evolutionary enigma迷. In their new study, Pollard et al. (2006) trawl用拖网捕鱼 the human genome and those of other mammals in search of short conserved保守的 DNA elements that show extremely rapid evolution only in humans. As they report in a recent issue of Nature, their scan yielded a gene for a novel新奇的 noncoding非编码的 RNA hat adopts采用 a human-specific structure and may regulate neurodevelopment. The completion of the human and chimpanzee大猩猩 genome sequences has provided opportunities for studying the evolution of Homo sapiens现代人的 in remarkably stimulating and systematic ways. How did our uniquely human features originate发源? How was the capacity for language, reason,and culture encoded in genes during evolution? Recent efforts in comparative genomics比较基因学 have begun to address such questions. Using a comparative genomics approach, Haussler and colleagues (Pollard et al., 2006) have now performed a genome-wide scan for regions highly conserved across mammalian genomes that appear to have undergone a sudden and rapid evolution in the human lineage世系. Molecular分子的 evolution occurs by several mechanisms机制. Sometimes, new genes can arise or vanish 消失spontaneously自发地 though this turns out to be surprisingly rare. More commonly, nonsynonymous非同义替换 changes in an amino 氨基的acid coding sequence confer 给予new biochemical properties性能 upon a protein, altering变更 its function. Alternatively, evolution can preserve a protein’s amino acid sequence but dramatically alter the spatial and temporal当时的 暂时的expression of the gene encoding 编码that protein. Previous attempts to elucidate 阐明genome evolution across species have focused on either the addition 添加or deletion遗失 of genes (Chimpanzee Sequencing and Analysis Consortium, 2005), because they are easy to recognize, or on changes in amino acid sequences