BIOL 112 1st Edition Lecture 7 Outline of Last Lecture I. Darwinian TheoryII. Darwin vs. MendelIII. Important TermsIV.Hardy-Weinberg EquilibriumV. Mathematical ModelingVI.Condition #1: Large PopulationOutline of Current LectureVII. Condition #2: No MutationsVIII. Condition #3: No Emigration or ImmigrationIX.Condition #4: Reproductive SuccessX. Mathematical Models of Natural SelectionXI.Different Types of SelectionXII. Allopatric SpeciationXIII. Physical Isolation Leads to Genetic IsolationCurrent LectureI. Condition #2: No Mutations•Mutations are the source of new alleles, they are rare and random (impossible to prevent)•Could change allele frequencies over a very long time, very slow process, could take thousands of generations•Probably not a significant factor in changes of allele frequency for most species, it’s subtle and takes a very long time (though it is highlysignificant as a source of new alleles)These 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.II.Condition #3: No Emigration or Immigration•Individuals carry alleles with them; if they leave, they change the al-lele frequency; if new people come it, they change the allele frequency•This is known as Gene Flow (people are carrying alleles with them) Does happen in many real populations in nature•This is the most difficult condition of the H-W Equilibrium to meetIII. Condition #4: Reproductive Success•(technically two conditions by Cambell. Combined by Aufderheide)•Genotypes (and resulting Phenotypes) do not influence competition success, mate selection, efficiency of mating, etc. — success in pass-ing genes to next generation•There is no natural selection (also not an easy criteria to meet)— genes influence many aspects of phenotypes and thus can have very subtle effects on reproductive success (helping or hurting)•Notice that not meeting any of Criteria #1 through #3 leads to allele frequency changes without selection : this is Non-Darwinian Evolution•Failure to meet Criteria #4 leads to allele frequency changes by selec-tion : this is Darwinian EvolutionIV.Mathematical Models of Natural Selection•Developed by Haldane, uses H-W equation plus a numerical estimate of selection: Relative Fitness•Relative Fitness: estimate of each genotype’s (phenotype’s) contribu-tion to the gene pool (represented by w)•w = 0 — no contribution (lethal)•w = 1.0 — best possible contribution•Fitness values 0 < w < 1.0•You can apply this “relative fitness” by solving a numerical formula to generate genotype frequencies for next generation (we are not doing this)•Fitness Calculations can be tested by measuring response of real pop-ulations to natural selection•Calculated that a tiny difference in fitness (1.0 vs. 0.999) can raise dominant allele frequency in population from 0.001 to 0.999 in just 10,000 generations•Haldane’s application makes the Hardy-Weinberg mathematics useful for predicting the evolutionary behavior of populations under various selective conditionsV. Different Types of Selection•Variability of population can be expressed graphically in a Gaussian “Bell Curve.” Statistical measures of a distribution include mean and standard deviation•Different types of selection affect different aspects of the bell curve:•Directional: selects against one end of range; shifts mean in direc-tion away from selection, does not change std. dev.•Stabilizing: selects against both extremes of range; does not af-fect mean, but reduces std. dev.•Diversifying (Disruptive): selects against the mean; splits popu-lation into bimodal form, double peaks on curve (two genetically distinct subpopulations)VI. Allopatric Speciation•How does natural selection produce two species from one?•Several models (ch. 24) exist, but we focus on Allopatric Speciation (“Classic Model”)•Species: Biological Species (Mayr) - the largest population that can in-terbreed with one another in nature and produce fertile offspring. Cannot successfully interbreed with other species•Largest unit in which gene flow is possible•Reproductive barriers: isolating mechanisms which permit different species to live in the same area but prohibit gene flow (they can’t re-produce together)•Prezygotic Barriers - before fertilization; habitat isolation, tempo-ral isolation, behavioral isolation, mechanical isolation, gametic isolation•Postzygotic Barriers - “yeah you have an egg and a sperm to-gether, but they’re not gonna work together for the better”; repro-duced hybrid viability, reduced hybrid fertility (produce organisms that are fertile i.e. mules), hybrid breakdown•Need at least one functional barrier type to prohibit gene flow (unableto mate) and sustain genetic differences between the two species•Two species must have enough genetic differences to create at least one barrier•Cline: Change in mean phenotype of populations of a species over its geo-graphical range. Related to climactic and physical differences over range. Reflects genetic differ-ences in populations over species’ range.•Deme: Smaller clusters ofindividuals within range. Population not uniformly distributed. Each cluster, a deme, is a small, local population. Organ-isms have higher probability of breeding within deme than between demes. (root of the word democracy — if that helps)•New species arise as a consequence of natural selection•If speciation depends upon enough genetic differences to produce a reproductive barrier, how is gene flow throughout a population pre-vented? Gene flow will abolish genetic differences among demes•Allopatric Speciation model initiates the process of speciation by physical isolation of a sub-population from the rest of the species•Physical isolation prevents gene flow between subpopulation and the rest of the species. Type of barrier depends upon characteristics of species being considered•How much time is “enough” for speciation?•Traditional view: Gradualism (Darwin’s original idea). Divergence process is slow. 1 mil - 10 mil years to make a species•Newer View: Punctuationalism (formulated in the 1970s) Diver-gence can be fast. Takes 100,000 - 1 mil years to make a speciesVII. Physical Isolation Leads to Genetic Isolation•Once physically isolated, several factors predispose the isolated popu-lation to become genetically distinct from the parent