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-<head>
-<title>Alignment Quality Annotation</title>
-</head>
-<body>
- <p>
- <strong>Alignment Quality Annotation</strong>
- </p>
- <p>Alignment Quality is one of the automatically calculated
- quantitative alignment annotations displayed below the columns of a
- multiple sequence alignment (and can be used to shade the
- alignment). It is an ad-hoc measure of the likelihood of observing
- the mutations (if any) in a particular column of the alignment.</p>
- <p>More precisely, the quality score is inversely proportional to
- the average cost of all pairs of mutations observed in a particular
- column of the alignment - a high alignment quality score for a
- column would suggest that there are no mutations, or most mutations
- observed are favourable.</p>
-
- <p>
- <em>The Algorithm</em><br> The quality score is calculated for
- each column in an alignment by summing, for all mutations, the ratio
- of the two BLOSUM 62 scores for a mutation pair and each residue's
- conserved BLOSUM62 score (which is higher). This value is normalised
- for each column, and then plotted on a scale from 0 to 1.
- </p>
- <p>Multiple alignment algorithms using the BLOSUM 62 substitution
- matrices should, in theory, maximise alignment quality for an
- un-gapped alignment, and locally maximise quality for gapped
- alignments.</p>
-</body>
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