Construction of Phylogenetic Trees

Construction of Phylogenetic Trees - a major character, a...

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Construction of Phylogenetic Trees Taxonomy is part of a larger division of biology known as systematics . Determination of phylogeny is a goal of systematics. This is done by the construction of phylogenetic trees, which in a sense represent evolutionary hypotheses and attempts to define monophyletic groups . To build these trees, we must have data, which comes from the characteristics used in classification. There are several methods of classification: traditional, phentic, and cladistic. They differ in how they value certain characters. Let's consider how traditional classification treats reptiles, birds, and mammals, as shown in Figure 3. Traditional Classification Data used in traditional systematics stresses both common ancestry (monophylesis) and the amount of divergence among groups. The traditional, dating to Linneaus view, is that birds have feathers, reptiles have scales, and mammals have hair. Using this as
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Unformatted text preview: a major character, a classification like that above has been constructed. Fossils , evidence of past life, are not included in this classification. Since all of these groups have the amniotic egg , or a modification of it, they would be united in a larger taxon. Linneus placed each of these groups in a separate class within the Phylum Chordata. A primitive character is one present in the common ancestor and all members of the group, such as the amniotic egg. A derived character is one found only in a particular lineage within the larger group. In our example above, hair and feathers may be viewed as derived characters. A traditional view of our example group is that birds and mammals evolved from reptiles due to their unique derived characters....
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