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Biology - Week 2 Notes

Biology - Week 2 Notes - Biology 2108 Summer 2008 Dr Davis...

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Biology 2108 – Summer 2008 – Dr. Davis Abbreviated lecture notes from the week starting 6/2/08 Corresponds with Chapter 23-24 in Campbell (7th Edition) 23 - The Evolution of Populations Genetic variations in populations provide the “raw material” on which natural selection can act. Although selection acts on individuals, it is the population that evolve. Population genetics is the study of how populations change genetically over time. Focuses on populations as the units of evolution Microevolution - Is change in the genetic makeup of a population from generation to generation Darwin lacked an satisfactory explanation for how heritable variation appears in a population and how this variation is transmitted to offspring The widely accepted view at the time was “ blending inheritance However, Darwin and others recognized this would actually eliminate variation! Gregor Mendel (Austria 1822-1884) A little known Augustian monk developed a theory of inheritance based on his experimental work with pea plants Mendel proposed a particulate model of inheritance a few years after Origin of Species was published. Darwin never read it, and it s implications were not understood by those that did read it! The Modern Synthesis The re-discovery of Mendel s work by several researchers in the early 20th century led to the rise of the modern synthesis The Modern Synthesis was a more comprehensive theory of evolution that reconciled Mendel s theory of inheritance and Darwin s Natural Selection into an integrated whole
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Gene Pools and Allele Frequencies Population - Is a localized group of individuals that are capable of interbreeding and producing fertile offspring Gene pool - the total aggregate of genes in a population at any one time Consists of all alleles at all gene loci in all individuals of the population Alleles - The variants of a particular gene that produce distinguishable phenotypic effects If only one allele exists at a particular gene locus then that allele is said to be fixed in the population. Phenotype - the physical, physiological, and behavioral traits of an organism, which are determined primarily by its genetic makeup. Genotype - The genetic makeup, or set of alleles, of an organism The Hardy-Weinberg Theorem Describes a population that is not evolving (Figs 23.4, 23.5, practice relevant problems at the end of chapter 23 ) States that the frequencies of alleles and genotypes in a population s gene pool remain constant from generation to generation provided that there is: Large population size No gene flow No mutations Random mating No natural selection Thus, Hardy-Weinberg equilibrium Describes a population where allele frequencies do not change Predicts that in a given population where gametes contribute to the next
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generation randomly, allele frequencies will not change.
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