Flavell R B
Philos Trans R Soc Lond B Biol Sci. 1986 Jan 29;312(1154):227-42. doi: 10.1098/rstb.1986.0004.
Most higher plant genomes contain a high proportion of repeated sequences. Thus repetitive DNA is a major contributor to plant chromosome structure. The variation in total DNA content between species is due mostly to variation in repeated DNA content. Some repeats of the same family are arranged in tandem arrays, at the sites of heterochromatin. Examples from the Secale genus are described. Arrays of the same sequence are often present at many chromosomal sites. Heterochromatin often contains arrays of several unrelated sequences. The evolution of such arrays in populations is discussed. Other repeats are dispersed at many locations in the chromosomes. Many are likely to be or have evolved from transposable elements. The structures of some plant transposable elements, in particular the sequences of the terminal inverted repeats, are described. Some elements in soybean, antirrhinum and maize have the same inverted terminal repeat sequences. Other elements of maize and wheat share terminal homology with elements from yeast, Drosophila, man and mouse. The evolution of transposable elements in plant populations is discussed. The amplification, deletion and transposition of different repeated DNA sequences and the spread of the mutations in populations produces a turnover of repetitive DNA during evolution. This turnover process and the molecular mechanisms involved are discussed and shown to be responsible for divergence of chromosome structure between species. Turnover of repeated genes also occurs. The molecular processes affecting repeats imply that the older a repetitive DNA family the more likely it is to exist in different forms and in many locations within a species. Examples to support this hypothesis are provided from the Secale genus.
大多数高等植物基因组包含高比例的重复序列。因此，重复DNA是植物染色体结构的主要组成部分。物种间总DNA含量的差异主要归因于重复DNA含量的差异。同一家族的一些重复序列以串联阵列的形式排列在异染色质位点。文中描述了黑麦属的例子。相同序列的阵列常常存在于许多染色体位点。异染色质通常包含几个不相关序列的阵列，并讨论了这些阵列在种群中的进化。其他重复序列分散在染色体的许多位置。许多可能是转座元件或由转座元件进化而来。文中描述了一些植物转座元件的结构，特别是末端反向重复序列。大豆、金鱼草和玉米中的一些元件具有相同的反向末端重复序列。玉米和小麦的其他元件与酵母、果蝇、人类和小鼠的元件具有末端同源性，并讨论了植物种群中转座元件的进化。不同重复DNA序列的扩增、缺失和转座以及种群中突变的传播在进化过程中导致了重复DNA的更新。文中讨论了这个更新过程及相关分子机制，并表明它们是物种间染色体结构差异的原因。重复基因也会发生更新。影响重复序列的分子过程表明一个重复DNA家族存在的时间越长，它就越有可能以不同形式存在于一个物种的许多位置。文中提供了来自黑麦属的支持这一假设的例子。
