Tree-building phylogenetic

Phylogenetic tree building seems to be more difficult for plants than for animals, and varying results have been reported even using the ancestral sequence approach 123,124). For the moment these trees must be considered only tentative. 

Tree-building methods implemented in available software are discussed in detail in the literature (Saitou, 1996 Swofford et al., 1996 Li, 1997) and described on the Internet. This section briefly describes some of the most popular methods. Treebuilding methods can be sorted into distance-based vs. character-based methods. Much of the discussion in molecular phylogenetics dwells on the utility of distance-and character-based methods (e.g., Saitou, 1996 Li, 1997). Distance methods compute pairwise distances according to some measure and then discard the actual data, using only the fixed distances to derive trees. Character-based methods derive trees that optimize the distribution of the actual data patterns for each character. Pairwise distances are, therefore, not flxed, as they are determined by the tree topology. The... 

Bininda-Edmonds, O.R.P., J.L. Gittleman, and A. Purvis (1999). Building large trees by combining phylogenetic information a complete phylogeny of the extant Carnivora (Mammalia). Biol. Rev. 74 143-175. 

The principal characteristics of the rRNAs and of their corresponding genes, as well as the advantages to study rRNA sequences, are summarized below. Then are surveyed the most important results obtained from comparisons of rRNA sequences for the building of the so-called universal phylogenetic tree, but also for the determination of the relationships between less distantly related species. 

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