Measuring Natural Selection by Populations
Measuring Natural Selection by Populations Biology201
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This 0 page Class Notes was uploaded by email@example.com Notetaker on Tuesday November 10, 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 19 views. For similar materials see Principles of Ecology and Evolution in Biology at Indiana University of Pennsylvania.
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Date Created: 11/10/15
Monday Nov 9 2015 Lecture 20 Chapter 23 Measuring Natural Selection in Populations 1 HardyWeinberg Equilibrium a In a population where gametes contribute to the next generation randomly and the Mendelian inheritance occurs allele and genotype frequencies remain constant from generation to generation b Describes hypothetical population that is not evolving i Five conditions for nonevolving populations b Natural populations can evolve at some loci while being in Hardy Weinberg equilibrium at other loci 2 Natural selection genetic drift and gene ow alter allele frequencies in a population 2 Natural Selection a Differential success in a reproduction results in certain alleles being passed to the next generation in greater proportions i DDT in fruit ies increased in frequency after DDT was used widely in agriculture b Adaptive evolution improvement 2 Genetic Drift a The smaller a sample the greater the chance of a random deviation from a predicted result i Signi cant in small populations b Describes how allele frequencies change unpredictably from one generation to the next i Reduces genetic diversity ii Changes allele frequencies randomly iii Can x harmful alleles b Affective pooulation size individuals that contribute to the population39s reproduction c Founder effect occurs when a few individuals become isolated from a larger population i Individuals moved by chance ii Allele frequencies different from the larger population b Bottleneck effect sudden reduction in population size due to a change in the environment ii Helps the understanding of how human activity affects other species b Greater Prairie Chicken i Loss of habitat caused a major reduction in population in Illinois ii Surviving birds had low level of variation iii Old DNA is used to compare pre and post bottlenecked population 2 Gene Flow a Consists of the movement of alleles among populations a b c d Alleles can be transferred through the movement of fertile individuals or games i Pollen Reduces variation among populations over time i Structured pooulations less gene flow Can decrease the tness of a population i Parus major bird on Vlieland island ii Immigration from the mainland introduces alleles that decrease tness on the island iii Natural selection removes alleles that decrease tness Can also increase the tness of a population i Spread of alleles for resistance to insecticides 1 Mosquitoes that carry West Nile virus and malaria ii Alleles have evolved in some populations that confer insecticide resistance to these mosquitoes Involves both chance and quotsortingquot i New genetic variation arise by chance ii Bene cial alleles are quotsortedquot and favored by natural selection Directional selection favors individuals at one extreme end of the phenotypic range Disruptive selection favors individuals at both extremes Stabilizing selection no extremes compromise intermediates 2 The Key Role of Natural Selection in Adaptive Evolution a b C d Striking adaptions in individuals with natural selection i Snake heads Increases the frequencies of alleles that enhance survival and reproduction Bc the environment can change adaptive evolution is a continuous process Genetic drift and gene ow do not consistently lead to adaptive evolution as they can increase or decrease the match between organism and its environment 2 Sexual Selection a b C Natural selection for mating success Sexual dimorphism marks difference between the sexes in secondary sexual characteristics Intrasexual selection direct competition among individuals for one sex often males for the opposite sex i Elkdeer ghting Intersexual selection often mate choice occurs when individuals of one sex are choosy in selecting their mates i Usually females ii Male showiness due to mate choice can increase a male39s chance of attracting a female while decreasing his chances of survival 2 Heterozygous Advantage Occurs when heterozygotes have a higher tness that either homozygotes i Stabilizing b Natural selection will tend to maintain two or more alleles at that locus c Sicklecell disease
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