Monday, March 23, 2015

Phylogenetic network of pairwise alignment methods

Phylogenetic networks can be used to illustrate the history of any set of objects or concepts, provided that this history is a divergent one (ie. the history is not simply the transformation of objects through time).

Since I have recently been writing about sequence alignments, it is worthwhile to show an example of applying a network to sequence alignment programs. This comes from the paper by Chaisson MJ, Tesler G (2012) Mapping single molecule sequencing reads using basic local alignment with successive refinement (BLASR): application and theory. BMC Bioinformatics 13: 238.

The authors discuss programs that map reads from a sample genome onto a reference sequence. They note: "the relationship between many existing alignment methods is qualitatively illustrated in the figure."

Their legend reads:
The applications / corresponding computational restrictions shown are: (green) short pairwise alignment / detailed edit model; (yellow) database search / divergent homology detection; (red) whole genome alignment / alignment of long sequences with structural rearrangements; and (blue) short read mapping / rapid alignment of massive numbers of short sequences. Although solely illustrative, methods with more similar data structures or algorithmic approaches are on closer branches. The BLASR method combines data structures from short read alignment with optimization methods from whole genome alignment.
The reticulation refers to their new program, which "maps reads using coarse alignment methods developed during WGA [whole genome alignment] studies, while speeding up these methods by using the advanced data structures employed in many NGS [next generation sequencing] mapping studies."

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