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Mechanisms of Evolution Guided Notes EVOLUTION • A change in ___________________ ___________________________ in a population over time ▫ There are different alleles for dark moths and light moths (B= dark, b= speckled) ▫ When pollution changes the environment, dark moths became more common, which means the allele that causes dark coloring became more frequent. ▫ This is _____________________________________! What is a population? • All the same species • Live in the same place at the same time • Can _________________________ Populations evolve, NOT _____________________________! • The genetics of a population can change based on genetic ____________________ that exist within a population ▫ Variations are caused by sexual reproduction and mutations • One individual cannot change its ___________________ • Evolution changes the gene pool of a population over generations Gene Pool • A GENE POOL - all of the ____________________ of the populations’ genes together in one large “pool” ▫ The larger the population the __________________ the gene pool Allelic Frequency • The percentage of any specific allele in the gene pool is called the ALLELIC FREQUENCY (ie: 70% dark alleles) Genetic Equilibrium • GENETIC EQUILIBRIUM refers to a population in which the frequency of alleles remains the ___________ over generations. • No ______________, so no evolution • You can use the Hardy-Weinberg equation to calculate the frequency of alleles in a population at equilibrium: ▫ p² + 2pq + q² = 1 But what drives change in a gene pool of a population? MECHANISMS OF EVOLUTION: HOW IT HAPPENS… Mechanisms of evolution: Natural Selection • ___________________ exists among individuals in a species. (Variation comes from mutations and sexual reproduction mixing genes from mom and dad) • Some variations are ____________________ and will help them compete better • Individuals that had advantageous variations are more likely to _____________________ and reproduce, while others without the variation are more likely to die (competition) • Over time, advantageous variations are passed down to future generations, changes accumulate and ___________________________ change Mechanisms of Evolution: Sexual Selection • Evolution of traits based on the ability to find mates • Traits will not help an individual survive, but will make them more likely to _________________________ and pass on their genes to future offspring • Proposed by Charles Darwin in addition to his theory of Natural Selection Phenotype/genotype • Natural selection and sexual selection work on the _______________________________ of organisms • Individuals with phenotypes that are better able to survive or attract mates will pass on their genetic information (genotypes) to their offspring • Since phenotype is determined by genotype, the alleles of a population will change as phenotypes change Mechanisms of evolution: Genetic Drift • A mechanism that can change a population’s genetic equilibrium is GENETIC ___________________ • The alteration of allelic frequencies by chance events (not selection) • Affects _________________ populations (small gene pools) Mechanisms of evolution: Gene Flow (Migration) • Genetic Equilibrium is also disrupted by the movement of individuals in and out of a population. • The transport of _________________ by migrating individuals is called GENE FLOW Mechanisms of Evolution: Population Bottleneck • If a population is reduced to just a few individuals, there is less genetic variation • Their offspring will also have __________ genetic variation • Genetic drift, gene flow, and population bottlenecks can significantly affect the evolution of small and isolated populations Results of Evolution • Changes in existing species, or possibly… • Entirely NEW species (Speciation) ▫ Occurs when members of similar populations can no longer interbreed and produce fertile offspring