Botanic Garden and Botanical Museum Berlin-Dahlem, Freie Universität Berlin, Berlin, Germany.
Plant Biol (Stuttg). 2011 Jan;13(1):185-93. doi: 10.1111/j.1438-8677.2010.00341.x.
Large-scale surveys of genome size evolution in angiosperms show that the ancestral genome was most likely small, with a tendency towards an increase in DNA content during evolution. Due to polyploidisation and self-replicating DNA elements, angiosperm genomes were considered to have a 'one-way ticket to obesity' (Bennetzen & Kellogg 1997). New findings on how organisms can lose DNA challenged the hypotheses of unidirectional evolution of genome size. The present study is based on the classical work of Babcock (1947a) on karyotype evolution within Crepis and analyses karyotypic diversification within the genus in a phylogenetic context. Genome size of 21 Crepis species was estimated using flow cytometry. Additional data of 17 further species were taken from the literature. Within 30 diploid Crepis species there is a striking trend towards genome contraction. The direction of genome size evolution was analysed by reconstructing ancestral character states on a molecular phylogeny based on ITS sequence data. DNA content is correlated to distributional aspects as well as life form. Genome size is significantly higher in perennials than in annuals. Within sampled species, very small genomes are only present in Mediterranean or European species, whereas their Central and East Asian relatives have larger 1C values.
大规模的被子植物基因组大小进化调查表明，祖先基因组很可能很小，在进化过程中 DNA 含量有增加的趋势。由于多倍体化和自我复制的 DNA 元件，被子植物基因组被认为具有“肥胖的单程票”（Bennetzen 和 Kellogg 1997）。关于生物体如何失去 DNA 的新发现挑战了基因组大小单向进化的假说。本研究基于 Babcock（1947a）在 Crepis 内部的核型进化的经典工作，并在系统发育背景下分析了属内的核型多样化。使用流式细胞术估计了 21 种甘菊属物种的基因组大小。进一步的 17 种物种的数据取自文献。在 30 种二倍体甘菊属物种中，存在着明显的基因组收缩趋势。通过在基于 ITS 序列数据的分子系统发育上重建祖先特征状态来分析基因组大小的进化方向。DNA 含量与分布方面和生活形式相关。多年生植物的基因组大小明显高于一年生植物。在所采样的物种中，只有地中海或欧洲物种具有非常小的基因组，而它们的中亚和东亚亲缘种具有更大的 1C 值。
