Eanes W F, Labate J, Ajioka J W
Department of Ecology and Evolution, State University of New York, Stony Brook 11794.
Mol Biol Evol. 1989 Sep;6(5):492-502. doi: 10.1093/oxfordjournals.molbev.a040565.
It has been proposed that the degree of recombination for a genomic region will affect the level of both nucleotide heterozygosity and the density of transposable elements. Both features of genomic diversity have been examined in a number of recent reports for regions undergoing relatively normal levels of recombination in Drosophila melanogaster. In this study the genomic variation associated with yellow-achaete-scute loci located at the tip of the X chromosome is examined by six-cutter restriction mapping. In this region, as usual for regions adjacent to telomeres, crossing-over is dramatically reduced, and published studies of visible mutants indicate extremely little restriction-map variation. Eight six-cutter restriction endonucleases were used to locate sequence variation in 14- and 16.5-kb regions in 109 lines sampled from North America, Africa, and Europe. The overall level of heterozygosity is estimated as 0.29%. Nine large insertions, all presumed to be transposable elements, were observed. Base-pair heterozygosity appears to be reduced compared with regions having normal levels of recombination. The estimated heterozygosity is much higher than reported in earlier studies of restriction-map variation among visible mutations in the complex. The incidence of large insertions is not elevated compared with that in other regions of the genome. This suggests that asymmetric synapsis and exchange is not an important mechanism for the elimination of transposable elements.
有人提出，基因组区域的重组程度会影响核苷酸杂合性水平和转座元件的密度。果蝇中一些近期报告已经对基因组多样性的这两个特征在经历相对正常重组水平的区域进行了研究。在本研究中，通过六切点限制酶切图谱分析来研究位于X染色体末端的黄-无刚毛-小盾片基因座相关的基因组变异。在该区域，如同通常与端粒相邻的区域一样，交叉互换显著减少，并且已发表的可见突变体研究表明限制酶切图谱变异极少。使用八种六切点限制内切酶来定位从北美、非洲和欧洲采集的109个品系中14 kb和16.5 kb区域的序列变异。杂合性的总体水平估计为0.29%。观察到九个大的插入片段，全部推测为转座元件。与具有正常重组水平的区域相比，碱基对杂合性似乎有所降低。估计的杂合性远高于该复合体中可见突变之间限制酶切图谱变异的早期研究报告。与基因组的其他区域相比，大插入片段的发生率并未升高。这表明不对称联会和交换不是消除转座元件的重要机制。
