Alignments and phylogenetic trees

Abstract

This chapter examines the concept of sequence alignment, which is the identification of residue-residue correspondences. It is the basic tool of bioinformatics. The chapter presents a comparison of pairwise sequence alignments and multiple sequence alignments. Multiple sequence alignments are much more informative than pairwise sequence alignments, in terms of revealing patterns of conservation. The chapter then looks at the process of constructing and interpreting dot plots, before considering the use of the Hamming distance and Levenshtein distance as measures of dissimilarity of character strings. It also explains the basis of scoring schemes for string alignment, including substitution matrices and gap penalties. Finally, the chapter studies the applications of multiple sequence alignments to database searching, before exploring the contents and significance of phylogenetic trees, and the methods available for deriving them.