Topics for Consideration

Topics for Consideration - Topics for Consideration...

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Topics for Consideration Evolution (18-20) Macroevolution versus microevolution; hox genes. Darwin’s theory of evolution: artificial (farmers) and natural selection: premise for natural selection to occur. What is natural selection? Stabilizing, disruptive, directional Measuring evolution, sedimentary rock and fossil layers, radioisotopic decay of atmospheric carbon, comparative anatomy (homologous and homoplastic structures and convergent evolution) vestigial structures, molecular evidence of genetic change. Biogeography and biogeographic realms Hardy Weinberg principle: genetic equilibrium – evolution in action by comparing expected with actual observations. Increasing and decreasing genetic variation: Decreasing: non-random mating, positive assortative mating, genetic drift, natural selection (stabilizing, directional, disruptive) Increasing: mutations, negative assortative mating, gene flow. Gene flow = opposite of genetic drift? Measuring genetic variation: Genetic polymorphisms: balanced polymorphisms (heterozygotic and frequency dependent selection) Balanced polymorphisms: a special type of genetic polymorphism in which two or more alleles persist in a population over many generations as a result of natural selection. Heterozygote advantage and frequency-dependent selection are mechanisms that preserve this. Heterozygote advantage: This means that Aa has an advantage. This is demonstrated in humans with sickle cell. The fitness of a particular phenotype might be dependent on how frequently it appears in the population. This is frequency dependent selection. Demonstrated in scale eating fish. Their frequency in the population flip flops constantly. Neutral variations Geographic variations Neutral variation is a variation that does not alter the ability of an individual to survive and reproduce. Geographic variations arise mainly in species that are separated over a large area.
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Biological species concept and speciation Biological species concept: first expressed by Ernst mayr. A species consists of one or more populations whose members interbreed in nature to produce fertile offspring and do not interbreed with different species. Evolutionary species concept: phylogenetic species concept. A population is declared a separate species if it has undergone evolution long enough for statistically significant differences in diagnostic traits to emerge. Reproductive barriers to prevent interbreeding between different species. Prevent gene flow. Prezygotic: gametic isolation, temporal isolation, behavioral isolation, habitat isolation, mechanical isolation. They prevent fertilization from taking place. An interspecific zygote can never be produced. Temporal isolation means that they reproduce at different times, and so their mating times do not coincide. Flies and frogs exhibit this.
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