BIOL 3350 1st Edition Lecture 15 Outline of Last Lecture I. Evolution in Small PopulationsII. Sampling BiasIII. Founder EventsIV. Population BottlenecksV. Genetic Drift Leads to FixationOutline of Current Lecture I. Overall effects of genetic driftII. Interaction of selection and driftIII. Interaction of drift with gene flowIV. Nonrandom matingV. GenotypesCurrent LectureI. Overall effects of genetic drifta. Changes in the distribution of genetic informationb. Variation within demes becomes variation among demesc. An allele can go to fixation or to extinction by chance alone; not a result of selectiond. This could make the organism less likely to survive t in the environmente. Promotes population subdivision and can result in speciationi. When the demes become different enough from each other, they are no longer able to interbreed and become different speciesII. Interaction of selection and drifta. Selection can fail in small populationi. Drift is another force like migration that can act against a favored allele and we don’t see it go to fixation the way we would expect based on fitness calculations aloneii. Population size is sufficiently small strong genetic driftiii. Selection is sufficiently weak cannot overcome the action of driftb. Outcome is often unpredictablec. Leads to effective neutralityd. If selection is stronger alleles will go to fixatione. If drift is stronger allele changes will fluctuate due to chance aloneIII. Interaction of drift with gene flowThese 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.a. Drift-migration equilibriumi. Balance between loss of alleles due to genetic drift and introduction of alleles from migrants1. When the gene flow and drift lines cross = drift-migration equilibrium2. Migration can be really important in small populations because it can counter the effects of drift and help small populations to maintain variabilityii. Gene flow prevents extinction of small populationsiii. Corridors for dispersal are critical in conservation management of small populations1. Two of these large reserves for Tigers in central India are connected by a long forest corridor and two of the other reserves were connected by another forest corridors the gene flow in those tigers that lived in those reserves were approximately the same as those in the ancient tigers in museums2. Genetic variability was less in those reserves without forest corridorsIV. Nonrandom matinga. Inbreeding - mating with closer relative; more common in a small populationi. Increases homozygosityii. Same allele can be passed from both parents1. Identical in state – if they have the same nucleotide sequence2. Identical by descent – if they are copies of the same allele from a common ancestoriii. Two heterozygote boxers breed will form an all white offspring which carries traits like blindness and deafness1. Cant get rid of the deleterious allele due to inbreeding (purebreeddogs)iv. Measure inbreeding with fixation index or coefficient of inbreedingv. Phenotypic consequences of inbreeding include inbreeding depression, which is a decline in the average fitness of a population due to exposure to deleterious recessive alleles in autozygous stateV. Genotypesa. Homozygous – if it has two alleles identical in stateb. Autozygous – if it has two alleles identical in descentc. Inbreeding increases homozygosity by adding more autozygous individuals to populationd. Inbreeding doesn’t change the allele frequencies from one generation to the next, but it does change the genotype
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