搜搜考试网哪位好心的人能帮我翻译下这篇文章,急,真心的感谢!
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哪位好心的人能帮我翻译下这篇文章,急,真心的感谢!
Recently, Bennett et al. (1997) produced a new database of 2802 nuclear DNA amounts by compiling data from five previously published lists (Bennett and Smith, 1976, 1991; Bennett, Smith and Heslop-Harrison, 1982; Bennett and Leitch, 1995, 1997). The database, which contains DNA C-values for just over 1 % of known angiosperm species, represents the largest database of nuclear DNA amounts available for any group of organisms. A histogram showing the frequency of genome sizes for these 2802 species reveals a strongly skewed distribution with a very small modal size of 0-7 pg ( 675 Mbp), well within the bottom I % of the ange. Thus, despite their very large range in nuclear DNA amounts and a maximum (127-4 pg) over 180-times he mode, most angiosperms (i.e. 517%) have small C-values between 0-1 and 35 pg, within only five-times the mode.
DISTRIBUTION OF DNA C-VALUES IN A PHYLOGENETIC CONTEXT
Previously, researchers have attempted to look for evolutionary trends in genome size at the species, genus and family level, yet no consistent correlations have been found. Both increases and decreases in genome size have been postulated to occur (e.g. reviewed by Stebbins, 1976; Price, 1988). However, with the exception of a few (e.g. Cox et al., 1998) these studies have been flawed by the lack of a rigorous phylogenetic framework on which to analyse the data.
It is now increasingly apparent that there is a phylogenetic component to quantitative genome size variation which should be evaluated before the evolutionary significance of C-value diversity can be fully explained (Pagel and Johnston, 1992; Bharathan, 1996). Two factors have recently made possible an investigation into the evolution of angiosperm C-values in such a phylogenetic context. First, as outlined above, the Angiosperm DNA C-values database now exists. Second, there is now a consensus about the broad phylogenetic relationships of the angiosperms. The phy-logeny is based on DNA sequence data from the plastid rbcL gene taken from Chase et al. (1993) together with additional data from the 18S nuclear ribosomal RNA gene (Soltis et al., 1997), the plastid atpB gene (Savolainen et al., 1996), and 252 non-molecular characters (Nandi, Chase and Endress, 1998). The phylogenetic tree divides the angiosperm families into four major categories of taxa-paleodicots, monocots, lower eudicots and higher eudicots, with Cerato-phyllales as sister to these four groups. These are not all monophyletic groups but they are useful from a descriptive standpoint. These are then further subdivided into 20 higher level groups . The robustness of this analysis has enabled us to examine how the large range of C-values is distributed throughout the angiosperms, and to see whether this sheds light on the sizes of the ancestral angiosperm genomes.
Recently, Bennett et al. (1997) produced a new database of 2802 nuclear DNA amounts by compiling data from five previously published lists (Bennett and Smith, 1976, 1991; Bennett, Smith and Heslop-Harrison, 1982; Bennett and Leitch, 1995, 1997). The database, which contains DNA C-values for just over 1 % of known angiosperm species, represents the largest database of nuclear DNA amounts available for any group of organisms. A histogram showing the frequency of genome sizes for these 2802 species reveals a strongly skewed distribution with a very small modal size of 0-7 pg ( 675 Mbp), well within the bottom I % of the ange. Thus, despite their very large range in nuclear DNA amounts and a maximum (127-4 pg) over 180-times he mode, most angiosperms (i.e. 517%) have small C-values between 0-1 and 35 pg, within only five-times the mode.
DISTRIBUTION OF DNA C-VALUES IN A PHYLOGENETIC CONTEXT
Previously, researchers have attempted to look for evolutionary trends in genome size at the species, genus and family level, yet no consistent correlations have been found. Both increases and decreases in genome size have been postulated to occur (e.g. reviewed by Stebbins, 1976; Price, 1988). However, with the exception of a few (e.g. Cox et al., 1998) these studies have been flawed by the lack of a rigorous phylogenetic framework on which to analyse the data.
It is now increasingly apparent that there is a phylogenetic component to quantitative genome size variation which should be evaluated before the evolutionary significance of C-value diversity can be fully explained (Pagel and Johnston, 1992; Bharathan, 1996). Two factors have recently made possible an investigation into the evolution of angiosperm C-values in such a phylogenetic context. First, as outlined above, the Angiosperm DNA C-values database now exists. Second, there is now a consensus about the broad phylogenetic relationships of the angiosperms. The phy-logeny is based on DNA sequence data from the plastid rbcL gene taken from Chase et al. (1993) together with additional data from the 18S nuclear ribosomal RNA gene (Soltis et al., 1997), the plastid atpB gene (Savolainen et al., 1996), and 252 non-molecular characters (Nandi, Chase and Endress, 1998). The phylogenetic tree divides the angiosperm families into four major categories of taxa-paleodicots, monocots, lower eudicots and higher eudicots, with Cerato-phyllales as sister to these four groups. These are not all monophyletic groups but they are useful from a descriptive standpoint. These are then further subdivided into 20 higher level groups . The robustness of this analysis has enabled us to examine how the large range of C-values is distributed throughout the angiosperms, and to see whether this sheds light on the sizes of the ancestral angiosperm genomes.
最近,班尼特等人.（ 1997年）制作了一个新的数据库,为2802细胞核DNA数额汇编数据,从五个先前公布的名单（班奈特和史密斯,1976年,1991年;班尼特,史密斯和heslop -哈里森,1982年;贝内特和leitch ,1995年,1997年） .该数据库,其中含有的DNA的C -值刚刚超过1 ％已知被子植物物种,代表了最大的数据库的细胞核DNA的金额可供任何一组的有机体.直方图显示频率的基因组大小为这些为2802种,揭示了强烈的分配倾斜与一个很小的模态的大小0-7编号（ 675人的MBP ） ,以及内部的底部i ％的昂热.因此,尽管他们非常大的范围内,在核DNA数额及最高（ 127-4 PG ）的超过180次,他的模式中,最被子植物（即517 ％ ） ,有小的C -值0-1之间和35编号,在短短的五年-倍模式.
分布的DNA的C -价值观在亲缘背景
此前,研究人员曾试图寻找演化趋势,在基因组大小在物种,属和家庭层面,还没有一致的相关性已被发现.既增加和减少基因组大小都被假定发生（如审查类型,1976年;价格,1988年） .但是,除少数国家（如考克斯等人,1998年） ,这些研究已经残缺,因缺乏严格的系统发育框架上的数据进行分析.
现在是愈来愈明显,是有亲缘成分,以定量基因组大小变异对其进行评估之前进化意义的C值多样性,可以充分解释（ pagel和约翰斯顿,1992年; bharathan ,1996年） .有两个因素,最近可能进行调查的演变被子植物的C -价值观,在这样一个背景下的亲缘.首先,正如上文所述,被子植物的DNA的C -价值观数据库目前存在的.第二,现在已经有了一个共识,对广大亲缘关系的被子植物.这种PHY - logeny是基于DNA序列数据,从质体rbcL基因取自大通等.（ 1993 ）连同额外数据,从18核糖体RNA基因（ soltis等人,1997年） ,质体atpb基因（萨沃莱恩等,1996 ） ,以及252名非分子特征（南,大通和endress ,1998 ） .亲缘树划分被子植物家庭分为四大类分类- paleodicots ,monocots ,降低eudicots和更高eudicots ,cerato - phyllales作为妹妹在这四个群体.这是不是所有的单系群体,但他们是有用的,从一个描述性的立场.这些都是再细分为20个较高水平的群体.在稳健的这项分析,使我们能够在研究如何把大范围的C值,是在全国范围内发行被子植物,以及看看这是否揭示了大小祖被子植物基因组中.
分布的DNA的C -价值观在亲缘背景
此前,研究人员曾试图寻找演化趋势,在基因组大小在物种,属和家庭层面,还没有一致的相关性已被发现.既增加和减少基因组大小都被假定发生（如审查类型,1976年;价格,1988年） .但是,除少数国家（如考克斯等人,1998年） ,这些研究已经残缺,因缺乏严格的系统发育框架上的数据进行分析.
现在是愈来愈明显,是有亲缘成分,以定量基因组大小变异对其进行评估之前进化意义的C值多样性,可以充分解释（ pagel和约翰斯顿,1992年; bharathan ,1996年） .有两个因素,最近可能进行调查的演变被子植物的C -价值观,在这样一个背景下的亲缘.首先,正如上文所述,被子植物的DNA的C -价值观数据库目前存在的.第二,现在已经有了一个共识,对广大亲缘关系的被子植物.这种PHY - logeny是基于DNA序列数据,从质体rbcL基因取自大通等.（ 1993 ）连同额外数据,从18核糖体RNA基因（ soltis等人,1997年） ,质体atpb基因（萨沃莱恩等,1996 ） ,以及252名非分子特征（南,大通和endress ,1998 ） .亲缘树划分被子植物家庭分为四大类分类- paleodicots ,monocots ,降低eudicots和更高eudicots ,cerato - phyllales作为妹妹在这四个群体.这是不是所有的单系群体,但他们是有用的,从一个描述性的立场.这些都是再细分为20个较高水平的群体.在稳健的这项分析,使我们能够在研究如何把大范围的C值,是在全国范围内发行被子植物,以及看看这是否揭示了大小祖被子植物基因组中.