Essay on Evolution and Natural Selection

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Biology Final Exam  Notes
Chapter 16
• Microevolution: Heritable change in the genetic makeup of a population
• Population: all individuals of a single species that lives together in the same place or time
• Polymorphism: the existence of discrete variants of a character
• Gene pool: the sum of all alleles at all gene loci in all individuals
• Genotype Frequencies: the percent og individuals possessing each genotype
• Phenotype Frequencies: The ratio of individuals with a particular phenotype to the total number of individuals in the population
• Allele Frequencies: the proportion of all copies of a gene that is made up of a particular gene variant (allele).
• Diploid: 2 basic sets of chromosomes
• Haploid: 1 basic set of chromosomes
• Null Model: predict what they would see if a particular factor had no effect o Serve as theoretical reference points against which observations can be evaluated
• Genetic Equilibrium: describes the condition of an allele or genotype in a gene pool (i.e. population) where the frequency does not change from generation to generation.
• Neutral Mutation: mutation that has no effect on fitness
• Gene flow: when organisms or their gametes sometimes move from one population to another. o If immigrants reproduce, they may introduce novel alleles into the population they’ve joined.
• Genetic Drift: chance events sometimes causing allele frequencies in a population to change unpredictably o Most common in smaller populations because only few individuals contribute to the gene pool and because any given allele is present in very few individuals o Generally leads to loss of alleles and reduced genetic variability
• Natural Selection: process by which such beneficial, heritable traits become more common in subsequent generations
• Sexual Selection: a form of natural selection established by male competition for access to females and by the females choice of males
• Sexual Dimorphism: differences in the size or appearance of males and females
• Inbreeding: a special form of nonrandom mating in which individuals that are genetically related, mate with each other.
• Balanced Polymorphism: 2 or more phenotypes are maintained in fairly stable proportions over many generations.
• Frequency Dependent Selection: term given to an evolutionary process where the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population.
• Neutral Variation Hypothesis: some of the genetic variation at loci coding for enzymes and other soluble proteins is selectively neutral
• Relative Fitness: the # of surviving offspring that an individual produces compared with the number left by others in the population
• Directional Selection: When individuals near 1 end of the phenotypic spectrum have the highest relative fitness
• Stabilizing Selection: When individuals expressing intermediate phenotypes have the highest relative fitness
• Disruptive selection: when extreme phenotypes have higher relative fitness that intermediate phenotypes

• Phenotype variation is brought about by continually mutating genes. the synthetic theory of evolution states that evolution is a two step process, the first is mutation of genes and the second is natural selection acting (and selecting from) the genes available. In short, phenotypic variation is caused by mutations, and natural selection tends to lessen variation (as those with preferable traits survive.)

• Genetic variation is what allows natural selection and more importantly new alleles to enter your population.

By having different genetic combinations, individuals of a population exhibit different traits which may or may not be to their benefit in regards to social and environmental interactions. Because of genetic variation, certain qualities are preferred over others due to a given surrounding and therefore change the allelic frequency towards