Haig David
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
Bioessays. 2016 Jun;38(6):549-55. doi: 10.1002/bies.201600003. Epub 2016 Apr 8.
Mitochondria exist in large numbers per cell. Therefore, the strength of natural selection on individual mtDNAs for their contribution to cellular fitness is weak whereas the strength of selection in favor of mtDNAs that increase their own replication without regard for cellular functions is strong. This problem has been solved for most mitochondrial genes by their transfer to the nucleus but a few critical genes remain encoded by mtDNA. Organisms manage the evolution of mtDNA to prevent mutational decay of essential services mitochondria provide to their hosts. Bottlenecks of mitochondrial numbers in female germlines increase the homogeneity of mtDNAs within cells and allow intraorganismal selection to eliminate cells with low quality mitochondria. Mechanisms of intracellular "quality control" allow direct selection on the competence of individual mtDNAs. These processes maintain the integrity of mtDNAs within the germline but are inadequate to indefinitely maintain mitochondrial function in somatic cells.
每个细胞中都存在大量线粒体。因此，自然选择对单个线粒体DNA促进细胞适应性的作用强度较弱，而有利于那些不考虑细胞功能而增加自身复制的线粒体DNA的选择强度较强。对于大多数线粒体基因来说，通过将它们转移到细胞核中，这个问题已经得到解决，但仍有一些关键基因由线粒体DNA编码。生物体通过管理线粒体DNA的进化来防止线粒体为宿主提供的基本服务发生突变退化。雌性生殖系中线粒体数量的瓶颈增加了细胞内线粒体DNA的同质性，并允许体内选择消除含有低质量线粒体的细胞。细胞内“质量控制”机制允许直接选择单个线粒体DNA的功能。这些过程维持了生殖系中线粒体DNA的完整性，但不足以无限期地维持体细胞中的线粒体功能。
