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Biol 102 notes 1

by: at19

Biol 102 notes 1 BIOL 102


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About this Document

These notes cover the introduction to evolutionary forces.
Biological Principles II
Dr. Sniegowski
Class Notes
Biology, evolutionary forces
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This 3 page Class Notes was uploaded by at19 on Tuesday January 26, 2016. The Class Notes belongs to BIOL 102 at University of Pennsylvania taught by Dr. Sniegowski in Spring 2016. Since its upload, it has received 13 views. For similar materials see Biological Principles II in Biology at University of Pennsylvania.


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Date Created: 01/26/16
 Modern definition of evolution o Change in the genetic composition of a population across generations o Individuals develop, they don't evolve o Change in average characteristics o Genetic composition of a population can be characterized by the frequencies of the alleles it caries o Thus, evolution = change in allele frequency across generations  Alleles are different forms of a gene  Has to do with things that are transmitted from one generation to another --> not in a moment of time  Allele frequencies o All allele frequencies at a given locus must sum to 1  Modern synthesis of evolutionary biology o Darwin-wallace idea of evolution by natural selection (1858) o Mendelian inheritance (early 1900s) o Theory and evidence on the forces that alter allele frequency (1918-1950)  Selection  Genetic drift  Migration  Mutation  4 evolutionary forces o Selection: the force that changes allele frequencies as result of fitness differences  Differences in reproduction/survival probability in a population  Fitness not equal to strength = how effectively you pass your genes on  It is the only force that causes the evolution of adaptive features of organisms o Genetic drift: random change in allele frequencies  How do you know it’s not a form of natural selection and isn't relaly "random?"  Occurs because populations are finite  Most pronounced in small populations o Migration (gene flow): change in allele frequencies that occurs when alleles move between populations  Migration is important in limiting divergence of populations within a species o Mutation: spontaneous change in the makeup of a genome  Cause changes in allele frequencies in populations, but typically v slow  The main importance of mutation is as the ultimate source of allelic variation that is acted upon by the other three forces o Calculating allele and genotype frequencies  N = total number of individuals in populations  2N = copies of alleles in population  Characterizing a diploid population for its allele and genotype frequencies at a single genetic locus wiht two alleles, A and a  Frequency of allele A = p = (2N(AA) + N(Aa))/2N  Frequency of allele a = 1-p = q (2N(aa) + N (Aa))/2N  Frequency of genotype * individuals = number of individuals that carry AA and aa o Hardy-Weinberg  Two populations can have the same allele frequencies but different genotype frequencies If no evolutionary forces are operating, mating is random  then it turns out that there is a single set of stable allele and genotype frequencies expected = hardy weinberg equilibrium and is illustrated in the next slide  Frequencies with HW  AA = p^2  Aa = 2pq  Aa = q^2 o Selection is the evolutionary force that produces adaptations  Variation for a trait --> differential survival and/or reproductive success (fitness) depending on trait value --> transmission of trait value to next gen (trait variaton must be heritable) --> change in allele frequencies, such that a higher proportion of a pop now exhibits the fitter trait value  Relative fitness in generation makes higher fitness alelle frequency goes up  Selection is an extremely powerful force  Carbonaria (the dark ones) moths o Dark color dominant o Carbonaria increased in frequency bc of a selective advantage in polluted areas o Tests:  Filming birds hunting from then  Mark-release-recapture in polluted and unpolluted  Twice the rate of recovery for preferred color environment (50% selective advantage) o Clear genetic basis (pollution)  Ex: human height is not  Nature vs nurture o Genotype + environment = phenotype o Not just dependent on genetic make up of organism (genotype)  Evolution by natural selection: quantitative traits o Natural selection cannot act directly on genotypes, but acts on phenotypes o There are a variety of patterns of selection, that depend on the relationship between phenotype and fitness o Changes in allele frequency at multiple gene loci are the basis for the evolution of quantitative traits


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