to Introduction Systematics Principles of Biology II GSU-Leege Systematics and Phylogeny:Uncovering patterns of evolution Classification of life's diversity Takes evolutionary relationships into account How shall we classify it? Systematics Systematics = anaytical approach to understanding diversity and relationships of organisms (present-day and extinct) Taxonomy: identification and classification of species (a part of systematics) Phylogenetics: classification based on evolutionary history Phylogenies based on Morphology (bone structure) Development (embryos) Biochemistry (DNA and other molecules) Records derived from living organisms fossils Taxonomy - employs the Linnaean system Carolus Linnaeus: 18th century Swedish botanist Contributions include Two part naming system (genus and specific epithet) Hierarchical classification wrote Systema Natura Before Linnean system Tradescantia ephemerum phalangoides tripetalum non repens Virginianum gramineum "The annual upright Tradescantia from Virginia with a grasslike habit, three petals, and stamens with hairs like spider legs" Tradescantia virginiana Taxonomy 1. Binomial nomenclature Genus (capitalized) followed by specific epithet (lower case) Italics or underlined Latin/Latinized (Ochisme, Marichisme, Peggichisme)
Improvement over common name b/c... Examples Homo sapiens Magnolia grandiflora Problems with common names In Minnesota - Red squirrel In Colorado - Chickaree
2. Hierarchical system Kingdom Phylum/Division Class Order Family Genus Species Objectives of Taxonomy distinguish close relatives arrange into broader categories Phylogenetics (another part of systematics) Definition: classification system based on evolutionary relationships Figure 25.9 The connection between classification and phylogeny Phylogenetics Cladistics techniques Build a cladogram (evolutionary tree) Descent from common ancestor in which new trait evolved Branch = group with shared synapomorphy characteristic: Nested classification Characteristics continue to change Cladistics and taxonomy Figure 25.11 Constructing a cladogram
Things to watch out for: Homology vs. analogy In constructing a phylogeny: distinguish whether a similarity is the result of homology or analogy Homology is similarity due to shared ancestry Analogy is similarity due to convergent evolution Homoplasy- analogous structure
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Cladistics Clades can be nested in larger clades, but not all groupings or organisms qualify as clades A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants LE 25-10a A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants LE 25-10b A polyphyletic grouping consists of various species that lack a common ancestor LE 25-10c Shared Primitive and Shared Derived Characteristics In cladistic analysis, clades are defined by their evolutionary novelties A shared primitive character is a character that is shared beyond the taxon we are trying to define A shared derived character is an evolutionary novelty unique to a particular clade Outgroups An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared primitive characteristics Outgroup comparison assumes that homologies shared by the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor It enables us to focus on characters derived at various branch points in the evolution of a clade Homework Complete Investigations Ch 25 on cd "How is Phylogeny Determined bu Comparing Proteins?"(do not submit for a grade) Chapter 25 Quiz (all appropriate questions - they're mixed up in the quiz)