UW-Madison BIOLOGY 101 - Microevolution (2 pages)

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University of Wisconsin, Madison
Biology 101 - Zoology 101: Animal Biology
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Zoology101 Animal Biology Last Lecture Outline Lecture 34 1 Why are there so many kinds of organisms 2 Process of evolution by natural selection Current lecture 1 Microevolution Microevolution Natural selection can provide a mechanism to create evolutionary change and help explain the existence of adaptations Microevolution variation in heritable traits within a population and differential survival and or reproduction change in traits in a population over time Population a localized group of individuals capable of interbreeding and producing fertile offspring Heritable traits traits with genetic basis genotype genetic composition of an individual phenotype observable characteristics Variations in genotype give rise to variation in phenotype selection acts on phenotype Alleles alternative versions of a gene that produce a different phenotypic event Microevolution change in allele frequencies in a population from one generation to the next Natural selection on phenotype by evolutionary change ultimately implies change in genotypes in a population Why is genetic variation important Variation is the raw material for evolution Environment and thus selection pressure is unlikely to remain constant Gene pool all of the alleles in a population Polymorphism where there are 2 or more versions of a trait within a population an allele becomes fixed when an entire population is homozygous at that locus Creating genetic variation mutation structure in gene or chromosome Sex combining existing alleles in new ways meiosis gamete formation fertilization Four basic processes causing change mutations occurrence of new mutation directly changes allele frequency relatively low mutation rates in most organisms generally neutral or have a small harmful effect genetic drift changes in allele frequencies between generations due to random events tends to reduce genetic variation through the loss of alleles can have a positive negative or no effect on population level of adaptation always present in some degree especially in a small population some can lead to large amounts of drift founder effect bottleneck effect may be particularly relevant for understanding how humans affect the viability of plant and animal population gene flow change in allele frequency between generations due to input of individuals or gametes e g pollen from other populations tends to reduce genetic variation among populations migration may have a positive negative or no effect on degree of adaptation on focal population Natural selection only one that shows a predictable high level of adaptation stabilizing disruptive diversifying directional Stabilizing favors individuals in the middle of phenotypic gradient Disruptive diversifying favors individuals at opposite ends of the phenotypic gradient directional favors individuals at one end of phenotypic gradient

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