BIOL 3350 1st Edition Lecture 14 Outline of Last Lecture I. Maintenance of Deleterious Mutation: Sickle-Cell AnemiaII. Migration = Gene FlowIII. Nature of Gene FlowIV. Genetic Consequences of migrationV. Migration rate (m)VI. Lake Erie Water SnakesOutline of Current Lecture I. Evolution in Small PopulationsII. Sampling BiasIII. Founder EventsIV. Population BottlenecksV. Genetic Drift Leads to FixationCurrent LectureI. Evolution in Small Populationsa. Genetic drift – random change in allele frequencies across generationsi. Change is not directed with respect to phenotypeii. Small populations are more subject to chance events iii. Certain alleles become more or less common by chance aloneiv. Sampling effect in small populations1. When population size is reduced some genetic variation is lost be chance2. Not all individuals in a population will reproduce every generationII. Sampling Biasa. The problem in small populations is sampling biasb. After one generation, the probability of staying at HWE is the minority à less than 20%c. Chance deviations because of small population sizesd. Certain genotypes will go extinct solely due to chance samplingIII. Founder Eventsa. Small number of individuals started the populationb. Examples: island populations or populations at the periphery of species’ rangesc. Genetic diversity cannot be contained in such a small populationd. Initial founder cannot carry all of the source populations’ genetic diversityThese 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.i. Ex: Lost locus B and alleles from locus A and C because the population was so smallIV. Population Bottlenecksa. Population size is drastically reduced due to some type disease or natural disasterb. Remaining survivors do not carryall the allelic diversity o the original populationc. The small amount of genetic diversity due to the small population size will eventually lead to fixation – random at which allele becomes fixedV. Genetic Drift Leads to Fixationa. Change in allele frequencies due to drifti. Impossible to predict within a single generation or population because change is randomb. What can be predicted?i. Effect of genetic drift among a group of demes1. Look at the effects of genetic drift among a number of small population, we can make some predictions about what happens to these groups of populations2. All have same starting conditions and then subject to genetic drift3. Each population will eventually fix of either allele A1 or allele A2, each goes to either 1 or 04. If we have a number of small population, we can predict how many of each one we will have in the end5. Natural selection is not having an effect in this situationc. Collared Lizards Studyi. Scientists studied this in collared lizards in Missouriii. Looked at effect of allele fixation in situations where natural selection wasnot acting on the alleles in focusiii. Looked at little, isolated populations in rocky areasiv. These alleles occur at almost equal frequencies all together of collared lizards in central USA, but this changed when they looked at the small, individual populations in Missouriv. Small populations without much migration between them, isolated so that the alleles have gone to fixation vi. Diversity has been lost in these small populationsvii. The graphs show that the smaller the population, the more quickly heterozygosity