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Modern Evolutionary Classification 18-2 I. Evolutionary Classification • • • A. Phylogeny – Scientist now group organisms into categories that represent lines of evolutionary decent or evolutionary relationships among organisms, not just by physical similarities. B. The higher the level of the taxon the further back in time are the common ancestor of all the organisms in that taxon. C. Animals that appear very similar may not share a recent common ancestor, at all. Example - Dolphin Plant Phylogeny Primate Phylogeny Animal (Invertebrate) Phylogeny Animal (Vertebrate) Phylogeny II. Classification Using Cladograms A. Cladistic Analysis – Identifies and considers only those characteristics that appear in recent parts of a lineage not in older members. These are called derived characters. Unique Characteristics ( these are used to construct cladograms.) 1. A diagram that shows evolutionary relationships among a group of organisms. Cladistics III. Similarities of DNA and RNA • A. The more similar the DNA sequence of two species , the more recently they shared a common ancestor and the more closely they are related in evolutionary terms. VI. Molecular Clock • • A. Uses DNA comparisons to estimate the length of time that two species have been evolving independently or have been separated. B. The longer in time 2 species descended from a common ancestor, the more different their genes are likely to be.