Ch 22 Descent with Modification A Darwinian View of life Monday June 09 2014 10 53 AM What is evolution and adaptation Evolution 2 main ideas Change over time of the genetic composition of a population Decent of modern organisms with modification from preexisting organisms Evolutionary adaptation Accumulation of inherited characteristics that enhance organisms ability to survive in specific environments 2 things needed for evolution Variation Competition Everyone is different Some people lose Pre Darwinian theory of evolution Lamarck Use disuse Bodies of living organisms are modified through the use or disuse of parts Inheritance of acquired characteristics These modifications are inherited by offspring Catastrophism Gradualism Uniformitarianism Cuvier catastrophism Catastrophism Catastrophes caused extinct species strata Hutton gradualism Lyell uniformitarianism Gradualism Slow natural forces wind water earthquakes volcanoes caused geological formations not catastrophes Uniformitarianism The mechanisms of change are constant over time Observations of geological formations rates processes occur earth much older than a few thousand years Evolution by Natural Selection Darwin and Wallace developed the theory independently Darwin Wallace Voyage of the HMS Beagle British naturalist in Indonesia Natural Selection The unequal survival and reproduction of organisms due to environmental forces resulting in the preservation of favorable adaptations Process selects from what is available in the gene pool E1 Notes Page 1 Process selects from what is available in the gene pool New characteristics are not created on demand Artificial Selection Selective breeding of organisms to encourage the occurrence of desirable traits Provides evidence for natural selection Trees vs Scala Naturae Aristotle s scala naturae Ladder of nature Evolution not about climning ladder of nature from lower to higher Evolution is a bush with lineages branching from one another Concept 22 3 Evolution is supported by an overwhelming amount of scientific evidence Homologous Analogous Structures Homologous Analogous Homologous structures Vertebrate Embryos Structures or other attributes in different species that resemble each other structurally but not necessarily functionally because of common ancestry Structures that are similar in function but NOT in structure and developmental and evolutionary origin All vertebrates share similar developmental genes Differences arise by some genes being switched on or off at varying times during development Biochemistry Molecular Biology DNA is universal genetic material All life forms use approximately the same 20 amino acids to make proteins All use ATP as the primary form of cellular energy All use RNA and ribosomes to make protein Convergent Evolution Convergent evolution Similarity between 2 organisms structures or molecules due to independent evolution along similar lines rather than descent from a common ancestor Analagous structures are the result of convergent evolution Ex Bat wing and butterfly wing Similar in function but not in structure Fossil Record Show change in organisms through time Change in types of organisms Past organisms differ from present day organisms Many species have become extinct Oldest species are in the deepest layers of strata E1 Notes Page 2 Ch 23 The Evolution of Populations Monday June 09 2014 11 54 AM The smallest unit of evolution One common misconception about evolution is that individual organisms evolve during their lifetime Evolutionary processes eg natural selection acts on individuals but populations evolve Concept 23 1 genetic variation makes evolution possible 2 main processes produce genetic variation Mutation Sexual recombination Changes in nucleotide sequence of DNA Source of new alleles and genes Point mutation Change in one nucleotide base in a gene Chromosomal mutations Delete disrupt or rearrange many genes on a chromosome Gene duplications Duplication of whole segments of a chromosome Mutation Mutations Sexual Recombination In sexually reproducing organisms sexual recombination produces most of the variability in each generation crossing over during prophase 1 of meiosis Variation within a population Discrete characters Classified on an either or basis Eg flower color in pea plants Quantitative characters Vary along a continuum within a population Eg height weight Concept 23 2 The Hardy Weibnberg equation can be used to test whether a population is evolving A group of individuals of the same species living in a certain defined area Populations Population Hardy Weinberg Equilibrium H W equilibrium Describes a population that is not evolving ie allele frequencies don t E1 Notes Page 3 Describes a population that is not evolving ie allele frequencies don t change 5 assumptions behind H W equilibrium No mutations Large population size No gene flow No natural selection Random mating Allele Genotype Frequencies Allele frequencies p frequency of allele 1 q frequency of allele 2 p q 1 Genotype frequencies P2 frequency of homozygous dominant q2 frequency of homozygous recessive 2pq frequency of heterozygotes p2 2pq q2 1 H W equation Concept 23 3 Natural selection genetic drift and gene flow can alter allele frequencies in a population Statistically the smaller a sample the greater the chance of deviation from a predicted result With small population sizes allele frequencies can fluctuate unpredictably from one generation to the next Tends to reduce genetic variation Genetic additions to or subtractions from a population resulting from the movement of fertile individuals or gametes Migration among populations Tends to reduce variation among populations over time Differential success in the reproduction of different phenotypes resulting from their interactions with the environment The contribution an individual makes to the hene pool of the next generation relative to the contribution of other individuals Genetic Drift Gene flow Natural selection Evolutionary Fitness Fitness 3 modes of selection Directional Disruptive Stabilizing Favors individuals at one end of a phenotypic range Favors individuals at both extremes of a phenotypic range Favors intermediate phenotypes and acts against extremes E1 Notes Page 4 Type of selection that favors a trait giving an individual a competitive edge in attracting or keeping a mate Intrasexual selection Direct competition among individuals of one sex for mates of the opposite sex Sexual selection
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