SGER/Collaborative Research: Character Weighting of Nucleotide Sequence Data

分子数据提供了帮助解决远亲生物体之间关系的可能性。核苷酸序列数据有可能特别具有信息性。但一个困难是，在序列中的任何一个位置只有四种字符状态(代表四种不同的核苷酸)。如果分子变化很快或发散时间很长，在任何特定位置的多个取代可能会模糊关于生物体之间关系的信息。如果我们知道哪些位置最有可能持续多次替换，我们可能会在分析关系时对该信息给予较低的权重。这个项目将测试一种确定哪些位置更有可能持续多次替换的方法。我们将获得一个开花植物家族中属的特定叶绿体基因的序列数据，并确定该家族中哪些核苷酸位置不同。然后，我们将从一些不同的被子植物家族中获得相同基因的序列数据，我们对这些家族的真实关系有一个合理的了解。我们将使用一个家族内核苷酸序列变异的信息来帮助确定哪些核苷酸位置提供了关于不同被子植物之间关系的准确信息。使用关于多重替代可能性的信息对关系进行分析的结果与真实关系的相似性将被用来评估该方法的效果。

Molecular data offer the possibility of helping to resolve relationships among distantly related organism. Nucleotide sequence data have the potential to be especially informative. But one difficulty is that there are only four character states (representing the four different nucleotides) at any one position in the sequence. If the molecule is changing rapidly or the time since divergence is long, multiple substitutions at any particular position may obscure information about relationships of the organisms. If we knew which positions were most likely to have sustained multiple substitutions we might give that information less weight in an analysis of relationships. This project will test one method of determining which positions are more likely to have sustained multiple substitutions. We will obtain sequence data of a particular chloroplast gene for genera within one family of flowering plants and determine which nucleotide positions vary within that family. We will then obtain sequence data of that same gene from a number of divergent angiosperm families for which we have a reasonable idea of the true relationships. We will use the information on variation in nucleotide sequence within one family to help decide which nucleotide positions provide accurate information on the relationships of the divergent angiosperms. The similarity of results of analyses of relationships using information on the likelihood of multiple substitution with the true relationships will be used to evaluate the efficacy of the method.