A framework for phylogenetic sequence alignment
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A phylogenetic alignment differs from other forms of multiple sequence alignment because it must align homologous features. Therefore, the goal of the alignment procedure should be to identify the events associated with the homologies, so that the aligned sequences accurately reflect those events. That is, an alignment is a set of hypotheses about historical events rather than about residues, and any alignment algorithm must be designed to identify and align such events. Some events (e.g., substitution) involve single residues, and our current algorithms can successfully align those events when sequence similarity is great enough. However, the other common events (such as duplication, translocation, deletion, insertion and inversion) can create complex sequence patterns that defeat such algorithms. There is therefore currently no computerized algorithm that can successfully align molecular sequences for phylogenetic analysis, except under restricted circumstances. Manual re-alignment of a preliminary alignment is thus the only feasible contemporary methodology, although it should be possible to automate such a procedure.