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Phylogeny and Systematics Chapter 26 Phylogeny Phylogeny – the evolutionary history of a species or group of related species. Systematics – The classification of organisms and determination of their evolutionary relationships (using fossils, molecules, genes...) Systematics Connecting Classification to Phylogeny Linnaen System of Taxonomy 2 main characteristics 2-part name (binomial) for each species Genus + specific epithet Underlined or italicized Genus is capitalized, specific epithet is not Hierarchical Classification of species into broader and broader groups of organisms. First level, and most specific, is species. Last, and most comprehensive, is domain. All levels beyond genus are capitalized. Category Domestic Cat Bobcat Lion Dog Specific epithet cattus rufus leo familiaris Genus Felis Felis Panthera Canis Family Felidae Felidae Felidae Canidae Order Canivora Carnivora Carnivora Carnivora Class Mammalia Mammalia Mammalia Mammalia Phylum Chordata Chordata Chordata Chordata Kingdom Animalia Animalia Animalia Animalia 2 main objectives of taxonomy To sort out and identify separate species. To order species into broader taxonomic categories. Taxon Taxon – The named taxonomic unit at any level Monophyletic – consists of an ancestral species and all its descendents (taxon=clade). Paraphyletic – consists of an ancestral species and some but not all of its descendents. Polyphyletic – includes taxa with different ancestors. Monophyletic Polyphyletic Paraphyletic Phylogenetic systematics based on cladistic analysis Phylogenetic systematics – classification based on evolutionary history. Fossil Record Anatomical Comparison Chemical/Molecular Comparison Cladistic Analysis evaluates information and applies it to tree building and classification (uses common ancestry as the primary criterion). Phylogenetic Tree/ Cladogram Branching diagram representing a hypothesis on the evolutionary history of a group of organisms. Branching does not indicate the ages of particular species, it only conveys patterns of descent. Location of branch points symbolize the relative times of origin for the different taxa. The degree of divergence between branches represents how different two taxa have become since branching from a common ancestor. Constructing a Cladogram Taxonomists classify species into high taxa based on the extent of similarities in morphology and other characteristics. Sorting Homology from Analogy Homology – likeness due to shared ancestry. Analogy – similarities due to convergent evolution, not common ancestry. Ex. bat and bird wings Convergent Evolution – similar environmental pressures and natural selection produce similar adaptations in organisms from different evolutionary lineages. Constructing a Cladogram Generally, the greater amount of homology, the more closely related the species are. The more complex two similar structures are, the less likely it is to have evolved separately or independently. Molecular Systematics Protein Comparison Primary structure of protein is genetically programmed. Similar amino acid sequence from different species indicates the genes for those proteins evolved from a common gene present in a shared ancestor. Molecular Systematics DNA Comparison Comparing the genes or genomes of two species is the most direct measure of common inheritance from shared ancestors. Molecular Systematics DNA Comparison Comparing the genes or genomes of two species is the most direct measure of common inheritance from shared ancestors. Paralogous genes – result from gene duplication, found in more than one copy in the same genome Ex. olfactory gene family in humans Orthologous genes – homologous genes found in different species because of speciation Ex. cytochrome c in humans and dogs Molecular Systematics **99% of the genes of humans and mice are orthologous. **50% of human genes are orthologous with genes of yeast. All living organisms share many biochemical and developmental pathways. Molecular Systematics Molecular Clocks Proteins evolve at different rates, although each type of protein evolves at a relatively constant rate over time. This information can be used to determine the relative time of the divergence of the modern species from the ancestral. The estimates are consistent with fossil evidence.
