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22 <head><title>Tree Calculation</title></head>
24 <p><strong>Calculation of trees from alignments</strong></p>
25 <p>Trees are calculated on either the complete alignment, or just the
26 currently selected group of sequences, using the functions in the
27 <strong>Calculate→Calculate tree</strong> submenu.
28 Once calculated, trees are displayed in a new <a
29 href="../calculations/treeviewer.html">tree viewing window</a>. There are
30 four different calculations, using one of two distance measures and
31 constructing the tree from one of two algorithms :
33 <p><strong>Distance Measures</strong></p>
34 <p>Trees are calculated on the basis of a measure of similarity
35 between each pair of sequences in the alignment :
37 <li><strong>PID</strong><br>The percentage identity between
38 the two sequences at each aligned position.
40 <li>PID = Number of equivalent aligned non-gap symbols * 100 /
41 Smallest number of non-gap positions in either of both sequences<br>
42 <em>This is essentially the 'number of identical bases (or
43 residues) per 100 base pairs (or residues)'.</em>
46 <li><strong>BLOSUM62, PAM250, DNA</strong><br>These options
47 use one of the available substitution matrices to compute a sum of
48 scores for the residue pairs at each aligned position. For details
49 about each model, see the <a href="scorematrices.html">list of
50 built-in score matrices.</a></li>
51 <li><strong>Sequence Feature Similarity</strong><br>Trees
52 are constructed from a distance matrix formed from Jaccard
53 distances between sequence features observed at each column of the
56 <li>Similarity at column <em>i</em> = (Total number of
57 features displayed - Sum of number of features in common at <em>i</em>)
58 <br />Similarities are summed over all columns and divided by
59 the number of columns. <br />Since the total number of
60 feature types is constant over all columns of the alignment,
61 we do not scale the matrix, so tree distances can be
62 interpreted as the average number of features that differ over
63 all sites in the aligned region.
66 </ul> Distances are computed based on the currently displayed feature
67 types. Sequences with similar distributions of features of the
68 same type will be grouped together in trees computed with this
69 metric. <em>This measure was introduced in Jalview 2.9</em></li>
72 <p><strong>Tree Construction Methods</strong></p>
73 <p>Jalview currently supports two kinds of agglomerative clustering
74 methods. These are not intended to substitute for rigorous
75 phylogenetic tree construction, and may fail on very large alignments.
77 <li><strong>UPGMA tree</strong><br>
78 UPGMA stands for Unweighted Pair-Group Method using Arithmetic
79 averages. Clusters are iteratively formed and extended by finding a
80 non-member sequence with the lowest average dissimilarity over the
84 <li><strong>Neighbour Joining tree</strong><br>
85 First described in 1987 by Saitou and Nei, this method applies a
86 greedy algorithm to find the tree with the shortest branch
88 This method, as implemented in Jalview, is considerably more
93 <p>A newly calculated tree will be displayed in a new <a
94 href="../calculations/treeviewer.html">tree viewing window</a>. In
95 addition, a new entry with the same tree viewer window name will be added in the Sort
96 menu so that the alignment can be reordered to reflect the ordering of
97 the leafs of the tree. If the tree was calculated on a selected region
98 of the alignment, then the title of the tree view will reflect this.</p>
100 <p><strong>External Sources for Phylogenetic Trees</strong></p>
101 <p>A number of programs exist for the reliable construction of
102 phylogenetic trees, which can cope with large numbers of sequences,
103 use better distance methods and can perform bootstrapping. Jalview
105 href="http://evolution.genetics.washington.edu/phylip/newick_doc.html">Newick</a>
106 format tree files using the 'Load Associated Tree' entry of the
107 alignment's File menu. Sequences in the alignment will be
108 automatically associated to nodes in the tree, by matching Sequence
109 IDs to the tree's leaf names.