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Unit 11 7F Analyze and evaluate the effects of other evolutionary mechanisms, including genetic drift, gene flow, mutation, and recombination. Let’s remember… • An allele is an alternative form of one gene B stands for black b stands for brown The allele would be… Genetic Drift • An evolutionary mechanism in which allele frequencies change in a population Allele frequency changes due to… • Natural disaster like flood, fire, or earthquake • A random change of the population (some are eliminated) • Different from natural selection b/c its by chance or randomly Original Pop Pop after change R = red star r = green heart 6R, 5r 5r Bottleneck Effect • The change in allele frequency where only genes of the surviving population members can be passed to future generations Gene Pool • the sum of all the genes in an interbreeding population Gene Pool • 2 blue alleles • 1 red allele • 12 green alleles Founder Effect • The change in allele frequency in a gene pool that changes from a large population to a small population • Ex: small number of individuals get separated from a larger population… the change in the allele frequency is the founder effect Founder Effect Gene Flow • Occurs when the genes of 1 population flow into a different population • This change causes a shift in allele frequency Immigration • Alleles move INTO a population Emigration • Alleles move OUT OF a population Lots of gene flow… • Slows down evolution • Lots of new alleles coming into and out of a population • More genetic variation within a population • Makes 2 populations more similar Lack of gene flow… • Less variation within a population • Makes 2 populations more different and separates them Mutation • Any change in the genetic material of a cell • Can occur within individual genes OR • Can involve changes in piece of chromosomes • If the mutation is beneficial to the organism, the mutation will be passed on to offspring • Slowly over time the mutation will become more common in a population Recombination • A source of heritable variation • Occurs for 2 reasons: a. Independent assortment b. Crossing over Independent Assortment Crossing Over Hardy-Weinberg Principle • States that allele frequencies in a population will remain constant unless one ore more factors cause those frequencies to change Hardy-Weinberg Equation Homozygous dominant 2 P Heterozygous Homozygous recessive + 2pq + 2 q = 1 p = dominant allele frequency q = recessive allele frequency Genetic Equilibrium • The situation in which allele frequencies remain constant (don’t change) • If frequencies don’t change, the population doesn't evolve Conditions required to maintain genetic equilibrium: 1. 2. 3. 4. 5. Random mating Population must be large No immigration or emigration No mutations No natural selection