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BIO 203 1st Edition Lecture 4 Outline of Last Lecture I. Mechanisms of Evolutiona. Mutationb. Gene Flowc. Natural Selectiond. Genetic Drife. Non-Random MatingII. Convergent Evolution Outline of Current Lecture I. How do biologists define a species?II.PhylogenyIII. Homoplasious vs. Homologous charactersCurrent LectureI. How do biologists define a speciesa. A species is composed of a group of interbreeding populationsb. Members of the same species can interbreed and produce viable, fertile offspringc. Biological Species Concepti. A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.ii. The ability to successfully interbreed is central to the conceptiii. Limits: Where do fossils fall in this category? Different species can sometimes breed ex. Liger). What about organisms that don’t have sex?d. Evolutionary Species Concepti. An evolutionary species is a single lineage of ancestor-descendant populationsthat maintains its identity from other lineages and that has its own evolutionary trajectoryii. This definition accommodates both sexual and asexual forms as well as fossils.II. Phylogenya. Evolutionary relationships between organismsb. Similarities and differences between species are products of their evolutionary historyc. Phylogenetic trees are a graphical representation of genealogical relationships between taxad. “Tree of Life” – all organisms related through descentThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Closely related species share more characteristics because of their more recent common ancestorse. Divergence- genetic drif or natural selection leads to populations being different enough that they no longer exchange genesf. Two branches with a most recent common ancestor are called sister taxag. Groups of close relatives form “clades” or monophyletic groupsh. A phylogeny is built from the study of characters that vary among speciesIII. Homoplasious vs. Homologous Charactersa. Homoplasious characters – similar characters developed independently from each other (through convergent evolution)i. Ex. The sugar glider from Australia and the flying squirrel from North America are not closely related but have very similar morphologyb. Homologous Characters – Character similarity that results from common ancestryc. Ancestral Character – the character state that was present in the common ancestord. Derived Character – characters that arose more recently than the common


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