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Population and Speciation
Population Genetics: The study of Evolution from a genetic point of view.
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Variations of Traits Biologists measure traits in large samples when studying variation. Bell curves show that average populations have similar traits. A few display the extremes of a trait. Varying genotypes arise in 3 ways Mutations from flawed copies of genes Recombination from an independent assortment of genes during meiosis Random fusion of gametes, combination of one sperm and one egg.
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Allele Frequency and the Gene Pool
Gene pool: the total genetic information available to a population Allele frequency: determined by dividing the number of a certain allele by the total number of alleles of all types in a population. Phenotype frequency: The number of individuals with a certain phenotype divided by the total number of individuals in a population.
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Harvey-Weinberg Genetic Equilibrium based on an ideal hypothetical population not evolving- This is not real life 1. no net mutations occur 2. individuals neither enter or leave a population 3. The population is large 4. individuals mate randomly 5. Selection does not occur
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Requirements for Genetic Equilibrium. Mutation:
Mutation: spontaneous mutation is slow over a longer period of time Mutagens force mutations from chemical or radiation exposure They produce new alleles that may be harmful or beneficial to a population
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Migration Immigration: the movement into a population
Emigration: the movement out of a population Gene Flow: the process of genes moving from one population to another.
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Genetic Drift The phenomenon by which allele frequencies in a population change as a result of random events or chance. Small populations experience a large amount of drift, they lose genetic diversity Large populations maintain a small amount of genetic drift
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Nonrandom Mating Random mating doesn’t always occur in a population because of geographic proximity Nonrandom mating is selection which may result in genes being to similar, which cause genetic disorders in a population Selection of a mate based on similar characteristics is assortative mating
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Natural Selection Members of a species more likely to pass on their genes to the next generation Stabilization selection: individuals with average form of a trait have the highest fitness Directional selection: individuals that have a more extreme form of a trait have a greater fitness than those with average form of a trait. Disruptive selection: individuals with extreme variation have greater fitness than the average form of a trait. Sexual selection: Males must be selected by females based on traits that are desired. The genes of successful reproducers not just survivors are amplified through natural selection.
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Concept of Species Speciation: Some species are very similar to their ancestral species while other populations become quite different Morphology: the internal and external structure and appearance of an organism Biological species concept: a species is a population of organisms that can successfully interbreed but can not breed with other groups.
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Isolating Mechanisms Geographic isolation: physical separation
Reproductive isolation: barriers to successful breeding between groups in the same area. Broad type: prezygotic-before fertilization and postzygotic-after fertilization
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Rates of Speciation Speciation may take millions of years, some may occur more rapidly, it may not occur smoothly and gradually. Punctuated equilibrium: a sudden shift in form that is often seen in the fossil record.
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