Schmid C W, Marks J
Department of Chemistry, University of California, Davis 95616.
J Mol Evol. 1990 Mar;30(3):237-46. doi: 10.1007/BF02099993.
The technique of forming interspecific DNA heteroduplexes and estimating phylogenetic distances from the depression in their duplex melting temperature has several physical and chemical constraints. These constraints determine the maximum phylogenetic distance that may be estimated by this technique and the most appropriate method of analyzing that distance. Melting curves of self-renatured single copy primate DNAs reveal the presence of components absent from the renaturation products of exactly paired sequences. This observation, which confirms existing literature, challenges a fundamental assumption: that orthologous (i.e., corresponding) DNA sequences in the divergent species are being compared in DNA heteroduplex melting experiments. As a model system, the thermal stabilities of heteroduplexes formed between a human alpha-globin cDNA and four alpha-like globin genes isolated from chimpanzee are qualitatively compared. The results of this comparison show that the cross-hybrids of imperfectly matched gene duplicates from divergent species can contribute to the additional components that are present in renatured single copy DNAs. Single copy DNA, as usually defined, includes sequence duplicates that will obscure phylogenetic comparisons in a mass hybridization of genomes.
通过种间DNA异源双链体的形成技术以及根据双链体解链温度的降低来估计系统发育距离，存在若干物理和化学限制。这些限制决定了可通过该技术估计的最大系统发育距离以及分析该距离的最合适方法。自我复性的单拷贝灵长类DNA的解链曲线显示，存在完全配对序列的复性产物中所没有的成分。这一观察结果证实了现有文献，对一个基本假设提出了挑战：即在DNA异源双链体解链实验中，正在比较不同物种中的直系同源（即对应）DNA序列。作为一个模型系统，定性比较了人类α-珠蛋白cDNA与从黑猩猩中分离出的四个α-样珠蛋白基因之间形成的异源双链体的热稳定性。该比较结果表明，来自不同物种的不完全匹配基因重复序列的交叉杂交体可导致复性单拷贝DNA中存在额外成分。通常定义的单拷贝DNA包括序列重复，这些重复会在基因组的大规模杂交中模糊系统发育比较。
