Evolution of Populations
Evolution of Populations Biology201
Popular in Principles of Ecology and Evolution
Popular in Biology
This 0 page Class Notes was uploaded by email@example.com Notetaker on Thursday November 5, 2015. The Class Notes belongs to Biology201 at Indiana University of Pennsylvania taught by Dr. Josiah Townsend in Fall 2015. Since its upload, it has received 21 views. For similar materials see Principles of Ecology and Evolution in Biology at Indiana University of Pennsylvania.
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Date Created: 11/05/15
Evolution of Populations 1 Genetic Variation makes evolution possible a Variation in heritable traits is a prerequisite for evolution i Populations evolve not individuals b Mendel39s work on pea plants provided evidence of discrete heritable units i Established quotgenesquot and dominant and recessive alleles 2 Genetic Variation a Genetic variation caused by differences in genes or other DNA segments b Phenotype product of inherited genotype and environmental in uences i Standing outside all day and being tangt does not cause tan children ii Differences can be determined by a single gene and classi ed on an eitheror basis iii Others are caused by 2 or more genes and vary Natural selection only acts on variation with a genetic component a Measured by gene variability or nucleotide variability i Nucleotide measures by comparing the DNA sequences of pairs of individuals 1 Rarely result In phenotypic variation b Average heterozygosity measures the average percent of loci that are heterozygous in a population i Having both allelesgtpq dominant and recessive i 2pq in the HardyWeinberg equation b Phenotypic plasticity i Change based on environmental in uences ii Only genetically determined variation can have evolutionary consequences iii Are not passed on to offspringgtonly genotype is passed on iv NOT ADAPTION 2 Sources of Genetic Variation a Mutationgene duplication cause new genes and alleles i Frame shift ii Deletion iii Duplication i NOT CAUSED BY EVOLUTION b Sexual reproduction results in genetic variation by recombining existing alleles c Formation of New Alleles i A mutation is random change in nucleotide sequences of DNA ii Only mutations in cells that produce gametes can be passed to offspring b Point mutation mutations that result in a change in protein production i Harmful ii Hidden from selection in recessive alleles iii Also can be bene cial sometimes iv Neutral variations no advantage or disadvantage 2 Rapid Reproduction a Mutation rates are low b Average is about one mutation in every 100000 genes per generation c Lower rates in prokaryotes and higher in viruses i Very short generation times 2 Sexual Reproduction a b Can shuf e existing alleles into new combination Recombination of alleles is more important than mutation 2 The HardyWeinberg Equilibrium a b C Population localized group of individuals capable of interbreeding and producing offspring Gene pool consist of all the alleles for all loci in a population i Loci locus spot on a gene ii A locus that is xed for all individuals in a population are homozygous for the same allele For diploid two alleles organisms the total number of alleles at a locus is the total number of individuals times 2 i P and q are used to represent the two alleles and their frequencies I 1 Diploid individuals can be either homozygous or heterozygous because there are two alleles to represent i Heterozygous both alleles dominant and recessive ii Homozygous two copies of one allele dominant and dominant recessive and recessive Example Population of wild owersgt number of copies of each allele i 320 red owers CRCR ii 160 pink owers CRCW iii 20 white owers CWCW 1 500 total ii CR320 times 2160800 iii C 20 times 2 160200 1 100 totals Frequency of each allele i PfreqCR800800200O8 ii qfreqC 20080020002 1 08021 2 HardyWeinberg Equation a Describes the genetic makeup we expect for a population that is not evolving i ldeal world ii Control in an experiment i P2 and q2the frequencies of the homozygous genotypes squared because pPPhomozygous dominant and qpphomozygous recessive ii 2pqthe frequency of the heterozygous genotype 2pqPpheterozygous In a population where gametes contribute to the next generation randomly and Mendelian inheritance occurs allele and genotype frequencies remain constant from generation to generation I Describes a hvpothetical population that is not evolving b 5 Conditions for nonevolving populations met in nature i No mutations ii Random Mating iii No natural selection iv Extremely large population size v No gene owno immigration or emigrations
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