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Science 24 March 2006:
Vol. 311. no. 5768, p. 1669
DOI: 10.1126/science.311.5768.1669d
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This Week in Science

Eukaryotic genomes are bloated with so-called "junk" DNA including introns, mobile elements, and large intergenic regions. Curiously, animal mitochondrial genomes are tiny, essentially junk-free, and conserved in gene structure, whereas plant mitochondrial genomes are relatively large, full of junk, and do not show a rigid conservation of gene structure. What underlies these very different patterns of genome size and complexity? Lynch et al. (p. 1727) review how mutation rates correlate with organelle genome complexity, being for the most part much higher in animal mitochondria than in plant mitochondria, which suggests that nonadaptive evolutionary forces play a critical role in shaping the structure of organelle genomes and possibly nuclear genomes. A stumbling block in annotating bacterial genomes is the presence of pseudogenes. Ochman and Davalos (p. 1730) review systematic methods for identifying pseudogenes in particular genomes, using the well-studied Escherichia coli as an example.




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