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Themes 5-8, Evolution and Stuff

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University of Calgary
BIOL 243
Heather Addy

Systematic Biology and Classification  Convergent evolution refers more to distantly related organisms and parallel evolution to more closely related ones. The evolution of flight is convergent between insects and vertebrates and parallel within the vertebrates  Systematics is used to reconstruct the phylogeny (evolutionary history) of a group of organisms and is portrayed as a phylogenetic tree. Systematics also assists in the identification and naming of species and their placement in a classification. A classification arranges organisms into hierarchical groups reflecting their relatedness  Phylogenetic trees can be used to distinguish similarities inherited from a common ancestor from those that evolved independently  A taxonomic hierarchy arranges organisms into ever more exclusive categories. In the Linnaean system, a family is a group of genera that closely resemble one another. Families are grouped into orders and so on.  Organisms are classified based on features such as morphological traits; chromosomal anatomy; gene sequences; details of physiological functioning; morphology of subcellelar structures, cells, and organ systems; and patterns of behavior Systematics: two goals-reconstruct phylogeny and taxonomy Phylogeny: evolutionary history of a group of organisms: presented as phylogenetic trees Ancestral characters – old forms of traits Derived characters – new forms of traits Outgroup comparison – comparing the group under study with more distantly related species Principle of monophyly: defines monophyletic taxa, each of which contains a single ancestral species and all of its decendents Polyphyletic taxa include species from separate evolutionary lineagesParaphyletic taxon includes an ancestor and some, but not all, of its decendents Assumption of parsimony: the simplest explanation is most accurate; any particular evolutionary change is an unlikely event and presumable happened only once in any evolutionary lineage Cladistics: produces phylogenetic hypothesis and classifications that reflect only the branching pattern of evolution Microevolution: heritable change in the genetics of a population eg. Antibiotic resistance in bacteria Population: all the individuals of a single species that live together in the same place and time Phenotypic variation: differences in appearances or function that are passed from generation to generation Quantitative variation: individuals differ in small, incremental ways eg. Mass of people Qualitative variation: exist in two or more discrete states eg. Snow geese have either blue or white feathers Polymorphism: the existence of discrete variants of a character Phenotypic variation can be due to genetics and environment Only genetically based variation is subject to evolutionary change Gene pool: the sum of all alleles at all gene loci in all individuals Genotype frequencies: the percentages of individuals possessing each genotype Allele frequencies: the relative abundances of the different alleles Null model: what would happen if a particular factor had no effect eg. Hardy Weinberg principle Hardy Weinberg Principle: conditions for genetic equilibrium, where neither allele frequencies nor genotype frequencies change in succeeding generations  No mutations  No migration  Infinite size  No selection  Random mating Mutation: heritable change in DNA Gene flow: migration of organisms or gametes (pollen) Genetic drift: chance events changing allele frequencies (small population) Population bottleneck: a stressful factor kills a lot of the population and eliminates some alleles Founder effect: few individuals colonize a distant locality and start a new population; they carry only a small sample of the parent population’s genetic variation Direction selection: individuals at one end of the phenotypic spectrum have the highest relative fitness; the trait’s mean value is higher or lower than before Stabilizing selection: Intermediate phenotypes have the highest fitness; reduces variation and increases the frequency of intermediate phenotypes Disruptive selection: extreme phenotypes have highest fitness; alleles producing extreme phenotypes become more common Sexual selection: intersexual selection: selection based on the interactions between males and females eg. Males produce otherwise useless structures to attract females; intrasexual selection: selection based on the interactions between members of the same sex eg. Males use their large body size, antlers, etc, to intimidate, injure or kill rival males Sexual dimorphism: differences in the size or appearance of males and females most likely as a result of sexual selection Balanced polymorphism: two or more phenotypes are maintained in fairly stable proportions over many generations; can be maintained by heterozygote advantage Frequency dependent selection: rare phenotypes have advantage Neutral variation hypothesis: some of the genetic variation at loci coding for enzymes and other soluble proteins is selectively neutral Biological Species Concept: defines a species as a group of organisms that can successfully interbreed and produce fertile offspring; does not account for species that reproduce asexually and for hybridizationPhylogenetic Species Concept: defines a species as a group of organisms bound by a unique ancestor Ecological Species Concept: defines a species as a group of organisms that share
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