TAILIEUCHUNG - Lecture Biology - Chapter 20: Genes within populations

This chapter students will be able to: Recognize that natural selection is the correct mechanism for explain evolution; understand the importance of and identify sources of genetic variation; know how to solve various problems associated with Hardy-Weinberg equilibrium; list the five factors, and state an example of each, that affect Hardy-Weinberg equilibrium and understand how each can produce evolutionary changes in a population experiencing any one of the five;. | Genes Within Populations Chapter 20 Darwin: Evolution is descent with modification Evolution: changes through time Species accumulate difference Descendants differ from their ancestors New species arise from existing ones Genetic Variation and Evolution Natural selection: proposed by Darwin as the mechanism of evolution individuals have specific inherited characteristics they produce more surviving offspring the population includes more individuals with these specific characteristics the population evolves and is better adapted to its present environment Natural selection: mechanism of evolutionary change Darwin’s theory for how long necks evolved in giraffes Natural selection: mechanism of evolutionary change Inheritance of acquired characteristics: Proposed by Jean-Baptiste Lamarck Individuals passed on physical and behavioral changes to their offspring Variation by experience not genetic Darwin’s natural selection: variation a result of preexisting genetic differences Lamarck’s theory of how giraffes’ long necks evolved Measuring levels of genetic variation blood groups enzymes Enzyme polymorphism A locus with more variation than can be explained by mutation is termed polymorphic. Natural populations tend to have more polymorphic loci than can be accounted for by mutation. DNA sequence polymorphism Gene Variation in Nature Godfrey H. Hardy: English mathematician Wilhelm Weinberg: German physician Concluded that: The original proportions of the genotypes in a population will remain constant from generation to generation as long as five assumptions are met Hardy-Weinberg Principle Five assumptions : No mutation takes place No genes are transferred to or from other sources Random mating is occurring The population size is very large No selection occurs Hardy-Weinberg Principle Calculate genotype frequencies with a binomial expansion (p+q)2 = p2 + 2pq + q2 p = individuals homozygous for first allele 2pq = individuals .

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