Wheeler Ward C
Department of Invertebrates, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024-5192, U.S.A.
Cladistics. 1990 Dec;6(4):363-367. doi: 10.1111/j.1096-0031.1990.tb00550.x.
Abstract- When divergent taxa are used to root networks, it is assumed that the character stales in the outgroup have historical similarity to those in the ingroup. Yet, if the data are nucleic acid sequences, the character stales shared by a divergent outgroup may be based not on history but on random similarity. A simple procedure is proposed to test this possibility. In the absence of an appropriate outgroup, root position can be estimated with the use of an asymmetrical character transformation matrix. If the matrix is sufficiently biased, it can supply the polarity information usually derived from an outgroup. This outgroup test and rooting procedure are demonstrated with ADH sequences from the genus Drosophila.
摘要——当使用不同的分类群来为网络确定根节点时，人们假定外类群中的性状状态与内类群中的性状状态具有历史相似性。然而，如果数据是核酸序列，一个不同的外类群所共有的性状状态可能并非基于历史，而是基于随机相似性。本文提出了一个简单的程序来检验这种可能性。在没有合适外类群的情况下，可以使用不对称性状转换矩阵来估计根节点位置。如果该矩阵有足够的偏向性，它就能提供通常从外类群得出的极性信息。本文用果蝇属的乙醇脱氢酶（ADH）序列展示了这种外类群检验和确定根节点的程序。
