BSC 2011 Unit III Study Guide1. Essentialism / Idealism! Plato: “God created all things”- everything had a constant, perfect essence “Ideal”- species do not change, no new species! ! ! Before evolution was suggested in 350 BC! - Aristotle: all living things are fixed in a linear hierarchyNatural Theology - study of nature to better understand God’s plan - Carolus Linnaeus (~1750): sought to discover order and classify the diversity of life to better understand God’s plan. Created the classification system. ! ! ! Before evolution was suggested in 350 BCCatastrophism- proponents usually accepted a divine creation- believed that the earth was “young”- fossil records reflect extinctions due to catastrophes, not evolution- George Curvier Uniformitarianism- mechanisms of geologic changes are constant over time- the same processes are operating today as in the past - Earth is very old- Charles Lyell- Lamarck 2. Evolution - species change over time and new species arise by the modification of earlier species Microevolution: gradual evolution of traits within a population of a species over time ! ex: beak of finchMacroevolution: evolution of an entirely new species! ex: arrive at new species of finch3. Artificial Selection: new species “created” from common ancestor via selective breeding by humans ! ex: “fancy” pigeons Comparative Anatomy: comparing the anatomy of different organisms supports the idea of descent with modification from a common ancestor ! ex: comparing limb bones despite their function [Homologous structure] Geology: geological features arise by slow gradual processes over long periods of time Paleontology: study of fossils; preserved evidence of previously living things; reveals mostly changes over time Comparative Embryology: early embryos of diverse but related groups share many features; as development proceeds, embryonic forms diverge and become more similar to adults of their own species4. Molecular Biology can provide evidence for evolution through protein and DNA sequence comparisons ! ex: Rhesus monkey has 95% of the same amino acids as humans 5. Analogous structures: same function but evolved independently ! ex: insect wing vs. bird wing Homologous structures: common evolutionary origin, but whose function may have changed “adapted” over time! ex: forelimbs in humans, birds, whales, cats Vestigial Structures: “remnants” of once functional ancestral structures! ex: human appendix, tail bone, goose bumps 6. Darwin found it intriguing how there were 14 different finches that evolved from a common mainland ancestor, each adapted to suit the conditions of their various islands Variety of finch beak size was what helped Darwin formulate his hypothesis7. Process by which populations evolve via natural selection:- within a population more offsprings are produced that can survive to reproduce; leads to competition for limited resources and struggle for existence- genetic variation exists in all organisms; some of this variation effects an individuals ability to survive and reproduce (who survives is not random)- “fittest” individuals produce more offspring and contribute more of their genes to the next generation - results in a change in the gene composition from one generation to the next with “favorable” characteristics accumulating over timeGenetic variation is required for evolution because it is the key factor for the “fittest” to survive and have a species evolve; without it there would not be a difference or change in a species, therefore, no evolution takes place8. Darwin’s views differed from Lamarck’s from that his theories made natural selection the key factor for evolution, instead Lamarck’s inheritance of acquired characteristics was a faulty mechanism, therefore, discredited 9. “Populations evolve, not individuals”! The meaning of this phrase is that individuals in a population vary, some are ! better able to survive and reproduce given a particular set of environmental ! conditions; these individuals generally survive and produce more offspring, thus ! passing their advantageous traits on to the next generation, overtime the ! population changes 10. There must be genetic variation for natural selection to occur because that’s the only way the “fittest” individuals will survive in the long run11. “Natural selection eliminated variation”! This phrase means that the better adapted overpower survival, therefore, ! decreasing variation in species 12. Mechanisms that act to maintain genetic variation in a populaton:- Genetic mechanism- meiosis and sexual reproduction: crossing over, independent assortment, random gamete fusion- diploidy and dominance: heterozygotes, recessive alleles are not expressed but remain in population pool- epistasis: can hide dominant allele from natural selection-Selection mechanism: some maintain rather than eliminate variation - polymorphism: when more than one form of a trait is evident among individuals ! in a population! ! Balancing selection: when natural selection maintains 2> phenotypic forms ! ! in a population (aka. balanced polymorphism)! ! ! Disruptive selection: in patchy environments maintains a balanced ! ! ! polymorphism ! ! ! ! ex: dark and light mice ! ! ! Frequency-dependent selection: fitness of a genotype depends on ! ! ! its frequency in the population - rare genotypes have a selective “advantage”- helps maintain genetic diversity! ! ! ! - helps prevent usual elimination of rare phenotypes by ! ! ! ! genetic drift mechanisms! ! Heterozygote advantage: when heterozygous genotypes have higher ! ! fitness than either homozygote, therefore, both alleles are maintained 13. Selectively “neutral” variation: genetic variation and polymorphism can be maintained in a population when nucleotide variations (alleles) do not affect fitness or reproductive success - gene pool: the total number of alleles of every individual in an interbreeding ! population- allele frequency: the frequency of an allele relative to that of other alleles of the ! same gene in a population! - genotype frequency: the frequency that a particular allele arises within a ! ! species- phenotype frequency: a ratio stating that number of times a specific phenotype occurs in a population in a single generation- gene fixation: the increase of the frequency of a gene by genetic drift
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