Cladistics - C1 PDF

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Cladistics C1...

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====== Phylogeny, Cladistics ====== Created Monday 20 April 2020

Taxonomists tend to fall into two schools, "Evolutionary" or "traditional" systematics versus "Phylogenetic" or "cladistic" systematics. Since the 1970s, "phylogenetic systematics" has been replacing "traditional systematics" Because the older literature and textbooks often use "evolutionary" classifications, the student must understand both systems. Old (morphology based) New (molecular evidence) Evolutionary taxonomists claim to recognize only "monophyletic" taxa, but use the term to include both holophyletic and paraphyletic taxa. Phylogenetic taxonomists also claim to recognize only "monophyletic" taxa, but limit the term to what is defined above as "holophyletic," although most reject that particular term. Both schools reject the use of polyphyletic taxa, although most phylogenetic taxonomists would use that term to included paraphyletic taxa.

Phylogenic Trees Scientist try to design a phylogeny that has the fewest changes, or nodes. (Parsimonious) Biology Terms Cladogram – A diagram used to represent a phylogeny, also called a phylogenetic tree. Phylogenetic Systematics – The branch of biology that classifies organisms using phylogenetic methods. Parsimonious – The simplest phylogeny, which has the fewest number of changes between groups of organisms. Phylogeny – A hypothetical relationship between organisms, represented by a cladogram. Symplesiomorphy – A characteristic that all organisms on a cladogram possess. Synapomorphy – A characteristic that only a specific group, descended from a common ancestor, possess. Homoplasy – A shared character that is shared through convergent evolution, not common decent. Systematics is the science of naming and classifying organisms in regard to their evolutionary relationships and comparative characteristics, it is often used interchangeably with the terms scientific classification and taxonomy.

the outgroup, as it is the least related organism, and is used to help distinguish the relatedness between the other groups. The basal group

A clade is a group of living organisms and the common ancestor they are derived from. Scientist use synapomophies, or shared derived characters, to define these groups. Symplesiomorphies, by contrast, are characters that all organisms in the cladogram have If the cladogram including the mammals was of all vertebrates, then the presence of vertebrae in our unknown animal would be a symplesiomorphy. Interpreting Cladograms {{.\Identical-cladograms.jpg}} ARE THE SAME In the following cladograms, it appears as if two different phylogenies are being presented. In the cladogram on the right, it appears that A is more closely related to C than in the cladogram on the left. This is simply a trick of presentation, but represents no meaning in terms of relatedness. These two cladograms do, in fact, represent a single phylogeny When creating or reading cladogram, it is important to remember that the only important features of the cladogram are the lines and the nodes...