BIOL 112 1st Edition Lecture 7 Outline of Last Lecture I Darwinian Theory II Darwin vs Mendel III Important Terms IV Hardy Weinberg Equilibrium V Mathematical Modeling VI Condition 1 Large Population Outline of Current Lecture VII Condition 2 No Mutations VIII Condition 3 No Emigration or Immigration IX Condition 4 Reproductive Success X Mathematical Models of Natural Selection XI Different Types of Selection XII Allopatric Speciation XIII Physical Isolation Leads to Genetic Isolation Current Lecture I 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 highly significant 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 meet III 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 passing 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 Evolution IV 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 conditions V 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 reproduce 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 reproduced 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 unable to 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 geographical range Related to climactic and physical differences over range Reflects genetic differences in populations over species range Deme Smaller clusters of individuals within range Population not uniformly distributed Each cluster a deme is a small local population Organisms 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 prevented 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 species VII Physical Isolation Leads to Genetic Isolation Once physically isolated several factors predispose the isolated popu lation to become genetically distinct from the parent population Isolated deme is frequently at the end of range so at the end of a cline Genetic content of deme already might not be representative of the whole population Isolated deme is usually small so genetic drift more likely found than in a large population Founder Effect Unusual frequencies of alleles in small