Chapter 26 Phylogeny and the Tree of Life Phylogeny evolutionary history of a species or a group of species Systematics discipline focused on classifying organisms and determining Taxonomy scientific discipline of naming and classifying organisms Dead languages so they didn t show preference for any particular language Specific epithet specific species Genus first part of a name evolutionary relationships o Used to construct phylogenies o Data fossils molecules and genes o Binominal nomenclature 2 part name Uses greek latin or latinized words Capitalized Always a noun Refers to a group of closely related organisms 1 or several species Cannot be used for more than 1 genus Both Always itilisized o Linnaean system name descriptor Cannot be used alone Never capitalized Adjective More than one species might have the same specific epithet Species genus family order classes phyla kingdoms domain Silly girls find only cadets packing kissable dicks o Taxon named taxonomic unit at any level Taxa are broader than genus are capitalized but not italicized o Comparison between taxa is not equal What is a species o Morphotype species based on particular distintive set of features not color Doesn t account for differences among populations Doesn t reflect behavoir or biochemistry o Biological species species is a geneticallly isolated set of populations that share a common gene pool in their natural environment and isolated from all other such groups Mayr Largest population within which effect gene flows occurs or can occur Anatomical behavior and physiological differences are only clues to the identification of genetically isolated groups Limitations Fossil species Asexual species Allopatric species breeding tests in the lab mihgt not be an accurate assessment Phylogenetic tree branching diagram that represents the evolutionary history of a group of organisms o Problems might occur when a more evolved version loses a developed trait making it look less evolved use DNA to solve problems o Linnaean system might classify but doesn t show relationships o Many want to move away from Linnaean system Phylocode classification based on evolutionary relationships Only name groups that have a common ancestor Groups no longer have ranks o The tree is a series of dichotomies branch points indicating a divergence o Sister taxa share an immediate common ancestor o Rooted means that the tree goes back to point o Basal taxon lineage that diverges early branches original near the common o Polytomy branch point from which more than 2 groups emerge evolutionary relationships among taxa not word ancestor o Trees Although organisms look similar we cannot see how or how quickly they evolved environment Branches don t actually indicate the age of a species just relative appearance order No assumptions on time speak can be made or how much change occurred in We cannot say that one taxon evolved from another just that they share a each lineage common ancestor Phylogenies are inferred from Morphological and Molecular Data Homologies phenotype and genetic similarities due to common ancestry Analogy when similar environmental processes and natural selection produces similar adaptations in organisms from different lineages homoplasties o Clue to telling between homology and analogy is the levels of complexity same with genes Molecular homoplasties similarities in sequence in not closely related organism Molecular systematics uses data from DNA and other molecules to determine evolutionary relationships Shared Characters used to Construct Phylogenetic trees o Cladistics using common ancestry to classify organisms o Clade groups of species that include an ancestral species and all descendants o Monophyletic group consists of an ancestral species and all of its descendants Clades nested in clades Taxon clade o Paraphyletic group ancestral species and some but not all descendants Shared Ancestral and Shared Derived Characters o Shared ancestral character character that originated in an ancestor of the taxon o Shared derived character shared by descendants but not found in ancestor evolutionary novelty unique to a clade Making a phylogenetic tree o Make character matrix Out group species group of species from a lineage that is known to have diverged before the lineage that includes the species being studied in group o Construct tree based on derived differences Some trees include a time scale in the length of the branches o Maximum parsimony simplest is usually right o Maximum likelihood given probability rules of how DNA changes over time a tree can be found that most likely represents the sequence of evolutionary events Phylogenetic trees are hypotheses o Phylogenetic bracketing use parsimony to predict the features shared by closely related organisms are present in the common ancestor and all of descendants unless data shows otherwise Organism s evolutionary history in its genome Molecular approach helps understand relationships unclear from just morphological study o Especially with organisms that are very unrelated Genes evolve at different rates o DNA for RNA r RNA changes slowly Used to compare taxa that diverged a long time ago o Mitochondrial DNA mt DNA evolves quickly Used to compare taxa that diverged more recently Gene duplication increases the number of genes in a genome o Gene families groups of related genes within a genome Results from gene duplication o 2 types of homologous genes Orthologous genes found in different species and divergence traces back to speciation events that created the species Can only diverge after speciation has taken place after genes are in different gene pools Paralogous genes homology results from gene duplication Multiple copies diverged from one another within a species Can diverge within a genome because there are more than one copies Olfactory genes Genome evolution o Lineages that diverged long ago share orthologous genes Commonalities explain why biochemical and developmental pathways are still shared among disparate organisms o Number of genes have no effect on perceived complexity Might be in the versatility of genes not the number of genes Molecular Clocks help Track Evolutionary Time Want to understand the relationship among all organisms even those not in the fossil record o Must rely on assumptions on the spread of change at the molecular level Molecular clock way to measure absolute time of evolutionary change based on the idea that some genes and other genomic regions
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