Understanding Diversity Systematics Chapter 23 Classification 23 1 Classifying Organism Systematics the scientific study of the diversity of organisms and their evolutionary relation ships taxonomy the science of naming describing and classifying organisms classification arranging organisms into groups based on similarities that reflect evolutionary re lationships among lineages St Augustine in the 4th century classified organisms as useful harmful or superfluous to Carolus Linnaeus designed a system of classification that grouped organisms according to their similarities mainly structural Linnaeus simplified classification developing a binomial system of nomenclature Binomial nomenclature each species is given a two part name The first part genus always capitalized second part specific epithet Both underlined or italicized Each taxonomic level is more general than the one below it Linnaeus developed this as humans well Drunk Kinky People Come Over For Great Sex Domain Kingdom Phylum Class Or der Family Genus Species Taxon is a formal grouping of organisms at any given level 23 2 Determining The Major Branches In the Tree of Life Bacteria have peptidoglycan in their walls which is not present in archaea Prokaryotes is divided into two major groups Bacteria Archaea Three domains Archaea Bacteria Eukarya three main braches of the tree of life Kingdoms Bacteria Archaea Fungi Plantae and Animalia No longer kingdom Protista supergroups emerged Some systematics prefer classifying organisms into clades Clades a group of organisms that share characters inherited from a common ancestor PhyloCode organisms are grouped into clades based on evolutionary relationships A species is defined as a segment of a population lineage Phylogenic trees represent hypothesized evolutionary relationships among organisms that have a common ancestor Cladogram a type of phylogenic tree where each branch represents a clade a group of organ isms with a common ancestor The node represents the divergence or splitting But the length of the branches does NOT tell you if the species evolved Other types of phylogenetic trees such as phylograms are able to indicate the relationship among taxa and indicate time or rate of evolution The length of the branches is propor tional to the amount of inferred change in characteristics Vertical Gene Transfer genes are transmitted from parent to offspring within the same species Horizontal Gene Transfer gene swapping between organisms in one taxon and unrelated organ isms in another taxon lateral gene transfer Evolution is not always linear Genes were not just passed down vertically but also ex changed laterally Horizontal Gene transfer can occur by exchange of DNA among different populations interbreeding and endosymbiosis 23 3 Reconstructing Evolutionary History Phylogeny the evolutionary history of a group of organisms from a common ancestor Phylogenies help understand evolutionary patterns identify new species and predict their characteristics Phylogenies are testable hypotheses Population made up of individuals of the same species that live in a particular area Biologists examine structural physiological developmental behavioral molecular traits and even fossil evidence to determine the relationship among species Homology refers to the presence in two or more species of a structure derived from a recent common ancestor Ex bones in the wing of a bat the paw of a dog and the hand of a human are homologous Similar structures develop when unrelated or distantly related species become adapted to similar environmental conditions Ex wings of a bat are used differently than wings on a butterfly Convergent evolution convergent evolution independent evolution of similar structures in dis tantly related organisms Reversal a trait reverses to its ancestral state It removes a similarity that had evolved Homoplasy a characteristic that superficially appears to be homologous but is actually indepen dently acquired by convergent evolution or reversal Shared ancestral characters plesiomorphies are features that were present in ancestral species and remain present in all groups descended from that ancestor Ex vertebral column Shared derived characters apomorphies are features that occur when two populations become separated and begin to evolve independently some of their homologous traits changes as well due to mutation natural selection and genetic drift These species can form a clade We identify all living things by their unique sequences of DNA or RNA Molecular se quences selected can be used as a genetic marker or a barcode to identify organisms This helps distinguish between species that look alike Molecular Systematics Focuses on molecular structure to clarify evolutionary relationships the more subunit sequences of two species corresponds the more closely related the species are considered to be Molecular clocks The ribosomes of archaea bacteria contain three types of RNA 5s 16s 23s cladograms show three types of taxonomic relationships monophyletic paraphyletic and polyphyletic monophyletic group shared derived characters that includes an ancestral species and all its de scendants ex having mammary glands three small bones in the middle ear and muscular diaphragm sister taxa sister groups share a more common ancestor with one another than either taxon does with any other group shown on a cladogram paraphyletic group is a group that contains a common ancestor and some but not all of its de scendants members of the group share ancestral characters polyphyletic group consists of several evolutionary lines that do not share the same recent com mon ancestor 23 4 Construction Phylogenetic Trees phenetic approach numerical taxonomy classification is based on the number of shared characters This does not distinguish between shared ancestral characters and shared derived characters cladistics phylogenetic systematics is approach in which organisms are classified based on recent common ancestry Do not use a heirarchy of taxa evolutionary systematic approach approach of systematics that uses the phenotypic similarities and combination of shared ancestral characters and shared derived characters to establish evolu tionary relationships and build classifications outgroup analysis a research method for estimating which attributes are shared derived charac ters in a given group of organisms outgroup is a taxon that represents an approximation of the ancestral condition but are seperated from the