Chapter 23 - Chapter 23 The Evolution of Populations 1 of...

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1 of 29 of 29 Chapter 23 Chapter 23 The Evolution of Populations The Evolution of Populations
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2 of 29 of 29 The Smallest Unit of Evolution The Smallest Unit of Evolution Individual organisms do NOT evolve, in the Darwinian sense, during their lifetimes Natural selection acts on individuals. Some individuals reproduce more, some less, but it is populations that evolve It is the genetic variations in populations that contribute to evolution Figure 23.1
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3 of 29 of 29 Population genetics Population genetics The study of how populations change genetically over time Microevolution A change in the genetic makeup of a population over time The modern synthesis Integrates Mendelian genetics with the Darwinian theory of evolution by natural selection Focuses on populations as the units of evolution
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4 of 29 of 29 Gene Pools and Allele Frequencies Gene Pools and Allele Frequencies A population i s a localized group of individuals that are capable of interbreeding and producing fertile offspring The gene pool is the total aggregate of genes in a population at any one time Consists of all gene loci in all individuals of the population MAP AREA ALASKA CANADA Beaufort Sea Porcupine herd range Fairbanks Whitehorse Fortymile herd range NORTHWEST TERRITORIES YUKON Figure 23.3
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5 of 29 of 29 The Hardy-Weinberg Theorem The Hardy-Weinberg Theorem Describes a population that is not evolving Assuming only Mendelian segregation and recombination of alleles occur, the frequencies of alleles and genotypes in a population’s gene pool will remain constant across generations Mendelian inheritance p reserves genetic variation in a population In a given population where gametes contribute to the next generation randomly, allele frequencies will not change ( Preservation of Allele Frequencies) Figure 23.4 Generation 1 C R C R genotype C W C W genotype Plants mate All C R C W (all pink flowers) 50% C R gametes 50% C W gametes Come together at random Generation 2 Generation 3 Generation 4 25% C R C R 50% C R C W 25% C W C W 50% C R gametes 50% C W gametes Come together at random 25% C R C R 50% C R C W 25% C W C W Alleles segregate, and subsequent generations also have three types of flowers in the same proportions
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6 of 29 of 29 Hardy-Weinberg Equilibrium Hardy-Weinberg Equilibrium Predicts the allele frequencies in the next generation, assuming certain conditions apply 1. Extremely large population size 2. No gene flow 3. No mutations 4. Random mating 5. No natural selection Describes a population where allele frequencies do not change These conditions are rarely met in nature and, therefore, allele frequencies rarely remain constant
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7 of 29 of 29 Using the Hardy-Weinberg Eq.
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This note was uploaded on 04/07/2008 for the course BIO 103 taught by Professor Mannino during the Fall '08 term at Long Island U..

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Chapter 23 - Chapter 23 The Evolution of Populations 1 of...

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