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MECHANISMS FOR EVOLUTION

MECHANISMS FOR EVOLUTION. CHAPTER 23. Objectives State the Hardy-Weinburg theorem Write the Hardy-Weinburg equation and be able to use it to calculate allele and genotype frequencies List the conditions that must be met to maintain Hardy Weinburg equilibrium. POPULATION SPECIES GENE POOL

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MECHANISMS FOR EVOLUTION

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  1. MECHANISMS FOR EVOLUTION CHAPTER 23

  2. Objectives • State the Hardy-Weinburg theorem • Write the Hardy-Weinburg equation and be able to use it to calculate allele and genotype frequencies • List the conditions that must be met to maintain Hardy Weinburg equilibrium

  3. POPULATION SPECIES GENE POOL GENE FLOW BOTTLENECK EFFECT FOUNDER EFFECT HETEROZYGOTE ADVANTAGE HYBRID VIGOR STABILIZING SELECTION DIRECTIONAL SELECTION DIVERSIFYING SELECTION SEXUAL DIMORPHISM VOCABULARY

  4. POPULATION • Localized group belonging to the same species • SPECIES • Naturally breeding group of organisms that produce fertile offspring • GENE POOL • Total aggregate of genes in a population at any one time Most species are not evenly distributed over a geographic range. Individuals are more likely to breed with others from their population center

  5. HARDY – WEINBURG THEOREM • Describes a NON-EVOLVING population • In the absence of other factors the segregation and recombination of alleles during meiosis and fertilization will not alter the overall genetic make-up of a population

  6. Imagine an isolated wildflower population with the following characteristics • Diploid with both pink and white flowers • Pink is dominant A and white is recessive a • There are 480 pink flowers and 20 white • 320 are AA • 160 are Aa (p + q)2 = 1 p + q = 1 p2 + 2pq +q2 = 1

  7. p2 = frequency of AA • 2pq = frequency of Aa • q2 = frequency of aa • Calculate q2 first • There are 1000 alleles • AA -- 320 x 2/plant = 640 • Aa --160 x 1/plant = 160 800 • aa -- 20 x 2/plant = 40 • Aa – 160 x 1/plant =160 • 200 • Frequency of A = 80% and a = 20%

  8. Condition for Hardy-Weinburg • Large population • No net mutation • Isolated population • Random mating • No natural selection

  9. MICROEVOLUTION LEADS TOMACROEVOLUTION

  10. CAUSES OF MICROEVOLUTION • GENETIC DRIFT • BOTTLENECK EFFECT • FOUNDER EFFECT

  11. GENE FLOW – genetic exchange between populations due to migration • Mutation – a new mutation that is transmitted in a gamete can immediately change the gene pool • NONRANDON MATING • Breed with other members of the “neighborhood” promotes inbreeding • Assortative mating – mate with others like themselves • NATURAL SELECTION

  12. Variation within Populations • Most heritable variation is measured by • Quantitative characters (vary along a continuum ie. Height) are polygenetic • Discrete characters (pink or white) are located on a single gene • Polymorphism – two or more forms of a discrete character are represented in a population

  13. GEOGRAPHICAL VARIATION A cline is a graded change in some trait along a geographical axis.

  14. MODES OF SELECTION

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