Birds have relatively few repetitive sequences compared to other groups of vertebrates; however, the members of order Piciformes (woodpeckers) have more of these sequences, composed mainly of transposable elements (TE). The TE most often found in birds is a retrotransposon chicken repeat 1 (CR1). Piciformes lineages were subjected to an expansion of the CR1 elements, carrying a larger fraction of transposable elements. This study compared patterns of chromosome distribution among five bird species, through chromosome mapping of the CR1 sequence and reconstructed their phylogenetic tree. We analyzed several members of Piciformes (Colaptes campestris, Colaptes melanochloros, Melanerpes candidus, and Veniliornis spilogaster), as well as Galliformes (Gallus gallus). Gallus gallus is the species with which most genomic and hence cytogenetic studies have been performed. The results showed that CR1 sequences are a monophyletic group and do not depend on their hosts. All species analyzed showed a hybridization signal by fluorescence in situ hybridization (FISH). In all species, the chromosomal distribution of CR1 was not restricted to heterochromatin regions in the macrochromosomes, principally pair 1 and the Z sex chromosome. Accumulation in the Z sex chromosomes can serve as a refuge for transposable elements. These results highlight the importance of transposable elements in host genomes and karyotype evolution.

中文翻译：

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啄木鸟（Aves Piciformes）中CR1样转座因子的分布：Z性染色体可作为转座因子的避难所。

与其他种类的脊椎动物相比，鸟类的重复序列相对较少。然而，象形目（啄木鸟）的成员具有更多的这些序列，主要由转座因子（TE）组成。在鸟类中最常见的TE是反转录转座子鸡重复序列1（CR1）。披甲形谱系经历了CR1元素的扩展，携带了较大比例的转座因子。这项研究通过CR1序列的染色体作图比较了五种鸟类之间的染色体分布模式，并重建了它们的系统树。我们分析了Piciformes（Colaptes campestris，Colaptes melanochloros，Melanerpes candidus和Veniliornis spilogaster）的几个成员，以及Galliformes（Gallus gallus）。Gallus gallus是已经进行了大多数基因组研究和细胞遗传学研究的物种。结果表明CR1序列是一个单基因组，不依赖于它们的宿主。分析的所有物种均通过荧光原位杂交（FISH）显示了杂交信号。在所有物种中，CR1的染色体分布不仅限于大染色体中的异染色质区域，主要是第1对和Z性染色体。Z性染色体中的积累可作为转座因子的避难所。这些结果突出了转座因子在宿主基因组和核型进化中的重要性。分析的所有物种均通过荧光原位杂交（FISH）显示了杂交信号。在所有物种中，CR1的染色体分布不仅限于大染色体中的异染色质区域，主要是第1对和Z性染色体。Z性染色体中的积累可作为转座因子的避难所。这些结果突出了转座因子在宿主基因组和核型进化中的重要性。分析的所有物种均通过荧光原位杂交（FISH）显示了杂交信号。在所有物种中，CR1的染色体分布不仅限于大染色体中的异染色质区域，主要是第1对和Z性染色体。Z性染色体中的积累可作为转座因子的避难所。这些结果突出了转座因子在宿主基因组和核型进化中的重要性。