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影响基因组大小的因素

上一篇 / 下一篇  2011-03-10 16:55:22

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  影响基因大小的因素

  熊荣川 译

  基因组大小(C值,每个单倍体基因组DNA的皮克pg数)在真核生物中,最大值和最小值相差200000倍多,在动物界中相差3000多倍。绝大多数的真核生物DNA都是非编码的,暗示大的基因组不一定就有更多数量的基因(Gregory, 2004)。大量非编码DNA的存在提出了一些关于与生物表型影响和基因组大小变化进化起源有关的问题,如“C悖论”(Gregory, 2001a)。基因组大小的演化经历了一个增加和减少的平衡,即由于可转移元件复制、插入导致基因组变大以及由于缺失及DNA修复机制而导致的基因组变小;另外,为了抵抗巨大缺失基因组也可能会容忍自身的增大(Petrov, 2001)。基因组大小变化的进化原因和结果还没有定论(Gregory et al., 1999; Petrov, 2001)。因为基因组的大小和蛋白质编码基因没有相关性,因此通常认为基因组中沉默基因(假基因)及自私的寄生元件的数量差异导致了基因组大小的不同(Ohno 1972; Pagel et al., 1992)。在一些生物中,基因组大小和细胞体积及细胞分裂速率呈正相关(Gregory, 2001a)。在高等分类阶元中,和基因组大小相关的因子更复杂,随着所研究的类群的不同而不同。在哺乳动物和鸟类中,新城代谢因素较为重要(Gregory, 2002a);在两栖动物中则不然(Licht et al., 1991; GREGORY, 2003),其基因组大小和发育速率、发育器官及发育的复杂性有一定的相关性,而在哺乳动物和鸟类中则没有这样的相关性(Gregory, 2002b)。

  关键词:C值 基因组大小

  原文:

  Genome size (C value, picograms of DNA per haploid genome) varies more than 200 000 fold among eukaryotes and 3000 fold among animals. Most eukaryotic DNA is noncoding,which implies that a large genome does not imply a large number of genes (Gregory 2004). The existence of large quantities of noncoding DNA raises several questions in relation to effects on the organismal phenotype and to evolutionary origin of variation in genome size, i.e., the “C value enigma” (see Gregory 2001a). Genome size evolves through a balance between duplication and insertion of transposable elements, which increase C values, and deletions and DNA repair mechanisms, which might decrease the C value or allow it to increase when preventing large deletion errors (Petrov 2001). The origins and the evolutionary consequences of variation in genome size continue to be debated (Gregory and Hebert 1999; Petrov 2001). Because genome size and the number of protein-coding genes are unrelated, it has been established that variation in genome size results primarily from variation in the amount of silenced genes (pseudogenes) and selfish parasitic elements (Ohno 1972; Pagel and Johnstone 1992). Genome size is positively related to cell volume and cell division rate in several groups of organisms (Gregory 2001a). At high taxonomic levels, the relationships seem to be more complex and highly dependent on the biology of the studied group. Metabolism is important in mammals and birds (Gregory 2002a), but not in amphibians (Licht and Lowcock 1991; Gregory 2003), and developmental rate and organ or developmental complexity are relevant in amphibians, but not in mammals and birds (Gregory 2002b).

  Key words: C value, genome size.

  参考文献:

  Genome size is not related to life-history traits in primates.pdf

  Gregory T. (2001a). "Coincidence, coevolution, or causation? DNA content, cellsize, and the C©\value enigma." Biological Reviews 76(1): 65-101.

  GREGORY T. (2003). "Variation across amphibian species in the size of the nuclear genome supports a pluralistic, hierarchical approach to the C-value enigma." Biological Journal of the Linnean Society 79(2): 329-339.

  Gregory T.R. (2002a). "A bird's-eye view of the C-value enigma: genome size, cell size, and metabolic rate in the class Aves." Evolution 56(1): 121-130.

  Gregory T.R. (2002b). "Genome size and developmental parameters in the homeothermic vertebrates." Genome 45(5): 833-838.

  Gregory T.R. (2004). "Macroevolution, hierarchy theory, and the C-value enigma." Paleobiology 30(2): 179.

  Gregory T.R.,Hebert P.D.N. (1999). "The modulation of DNA content: proximate causes and ultimate consequences." Genome research 9(4): 317.

  Licht L.E.,Lowcock L.A. (1991). "Genome size and metabolic rate in salamanders." Comparative Biochemistry and Physiology Part B: Comparative Biochemistry 100(1): 83-92.

  Petrov D.A. (2001). "Evolution of genome size: new approaches to an old problem." Trends in Genetics 17(1): 23-28.


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