分子进化研究中的今祖法,其理论基础、存在的问题和解释  

THE ESSENCE OF THE PRESENT-DAY ANCESTOR METHOD FOR CONSTRUCTING EVOLUTIONARY TREES FROM SEQUENCE DATA AND THE PUZZLE ENCOUNTERED IN APPLYING THIS METHOD

作　　者：李靖炎[1] Li Jingyan(Kunming Institute of Zoology,Academia Sinica,Kunming,Yunnan)

机构地区：[1]中国科学院昆明动物研究所

出　　处：《Zoological Research》1988年第2期141-150,共10页动物学研究（英文）

摘　　要：在分子进化树的建立上,今祖法(Present-Day Ancestor Method)由于能够避免由于不同进化枝进化速率的不同所造成的错误,对于相距较远的各类群低等生物的进化关系的研究有着特别重要的意义。但是在应用此法于具体的研究时,也遇到了一些令人困惑的带根本性的问题。为此我们对它的理论基础、适用范围和所遇到的问题等等进行了一番认真的考察,并对存在的问题给予了合理的说明。The essence of the present-day ancestor method was analyzed. This method is useful especially in studying the phylogenetic relationships among distantly related groups from sequence data, because the mistakes produced by simple clustering analysis resulting from the unequal rates of evolution may be avoided. The essence of this method is that the difference matrix of the phylogenetic tree with unequal rates is transtormed into a new matrix, which is corresponding to an evolutionary tree having the same topology, but with equal rates. The basic correcting factors used in this method are actually the sequence differences between the mulecules of those species, of which we want to study the phylogenesis, and the molecule of their common ancestor. If these correcting values are added or subtracted by any numerical value equally, the final result will not be changed in topology. If we use the molecule of a present-day species as reference to replace that of the unknown ancestor, it just means that the correcting values are added equally by a value representing the sequence difference between the ancestor and the reference, and therefore the final result will not be changed either. There is one thing to be worth notice: in the light of our tests, it would be best if the species used as reference is outside the evolutionary tree, which is being probed. When the present-day ancestor method was applied to specific research, a perplexing fact was encountered: from the same one difference matrix a series of different trees could be obtained when different species were successively used as references. This fact is completely contradictory to the theoretical deduction. After having carried out a series of tests, the author reached a conclusion that the puzzle was brought about by the various coincident relationships between the molecules of the reference species and the of those species we want to study When one reference species was replaced by another, the concrete coincident relationship altered, and the final result might

关 键 词：分子进化 系统树 今祖法 偶合 

分 类 号：G63[文化科学—教育学]