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Unformatted text preview: 1 The Origin of Species • In 1942, Ernst Mayr A is defined as an evolutionarily indep endent p op ulation or gro up of p op ulations. • A sp ecies is defin ed as a group of p op ulations whose members h ave the p otential to interbreed in n ature and p roduce v iable, fertile offsp rin g but who cannot p roduce viable, fertile offsp rin g with other such p op ulations. • A biological species is the largest set of populations in which genetic exchange is possible and that is genetically isolated from other populations. • Species are based on interfertility, not physical similarity. • Humans have considerable diversity, but we all belong to the same species because of our capacity to interbreed. • When gene flow is reduced between populations, they may then diverge genetically as a result of mutation, natural selection, and genetic drift. • This genetic divergence may eventually lead to , the creation of new species. • Usually, speciation creates two or more distinct species from a single ancestral group. • Gene flow elimin ates genetic differences amon g p op ulations, so evolutionary indep endence starts with lack o f gen e flow. • consists of adap tations that evolve within a p op ulation, confin ed to one gene p ool. ( eg, mutation, genetic drift, natural selection and gene flow) • refers to evolutionary chan ge abov e the sp ecies level (such as the ap p earance o f evolutionary novelties (e.g., feathers and flight in birds) that can be used to define high er taxa.) • Microevolution is simp ly a chan ge in gen e frequ ency within a p op ulation. • Evolution at this scale can b e observed ov er short p eriods of time between one gen eration and the next • E.g mosqu itoes evolv in g resistance to DDT • whiteflies evolv in g resistance to pesticides • gonorrheal bacteria strains evolvin g resistance to p enicillin • HIV strains evo lvin g resistance to antiviral m edicines There are a few basic ways in which microevolutionary change happens. •Mutation, • migration, •genetic drift, and natural selection are all processes that can directly affect gene frequencies in a population How Are Species Defined and Identified? species Introduction s pe ciation Large ground finch M edium ground finch An ancestral population Ancestral population splits into separate populations, which occupy dif er ent islands Descendant populations evolve in dif eren t environments, thei r characteris tics diverge Evidence for speciation: experiment Microevolution Macroevolution Microevolution T h e s e H ap py fa c e spi de rs look di ffer e nt b ut ar e a l th e sa m e sp e ci es - th e y ca n i nt e rbr e ed . No m at er how diverse the individuals look - they rem ain m em bers of the sam e species Fruit flies from a single population w ere divided into separate populations living in different cages to simulate geographic isolation....
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This note was uploaded on 01/18/2010 for the course BIO SCI 104 taught by Professor Lin during the Spring '09 term at UC Davis.
- Spring '09