Chapter 23

Chapter 23 - Chapter 23 Evolution of populations Chapter...

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Chapter 23 Evolution of populations
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Chapter outline Production of variation Hardy Weinberg Population genetics Natural selection, genetic drift, gene flow as mechanisms of evolution Difference between adaptive evolution and evolution
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Genetic Variation, where does it come from?
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Variation produced by Mutation Where new alleles come from Sexual Reproduction The reshuffling of all those alleles to make new combinations Those heritable combinations are what selection acts on to mold populations
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The Modern Synthesis How can particulate inheritance be responsible for quantitative traits The melding of Mendelian Genetics with continuous (quantitative) variation Early to mid 20 th century Dobzhansky, Wright, Fisher, Haldane, Mayr, etc. Population Genetics comes from this
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Characterizing Variation Variation along a continuum we call quantitative variation Quantitative characters are traits such as height, skin color… Remember, multiple genes with multiple alleles each contributing to a single trait produce these types of characteristics
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Genetic variation Populations can vary at the genetic and molecular level We can be talking gene (allelic) variation Products that the gene codes for (enzymes, proteins, traits) Nucleotide level-differences in actual DNA sequences Average Heterozygosity
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Average Heterozygosity One way to describe genetic variation The average number of genes an individual is heterozygous Fruit fly-13,700 genes Average fruit fly is heterozygous for 1,920 loci (genes) Heterozygosity = 1,920/13,700 = 0.14 = 14%
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Heterozygosity can be measured Gel electrophoresis Measures the different allozymes (enzymes) in a population These are the protein products This is genetic variability PCR Measures actual nucleotide variation (variation in sequences of DNA) Nucleotide Variability
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Variation within a population AA Aa aa AA AA Aa AA AA Aa AA AA Aa AA AA Aa aa AA AA AA aa AA AA Aa AA AA Aa AA AA Aa AA AA Aa aa Aa AAAA Aa aa AA AA Aa AA AA Aa aa AA AA Aa AA Aa aa AA AA Aa AA aa Aa aa AA AA Aa AA
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Variation between populations AA AA Aa aa aa Aa Aa A a aa AA AA AA Aa aa aa Aa Aa A a aa AA AA AA Aa aa aa Aa AA AA Aa aa aa Aa Aa AA AA AA Aa aa aa Aa Aa A a aa AA AA AA Aa aa aa Aa AA AA Aa aa aa Aa Aa aa AA Aa aa aa AA aa AA Aa
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Variation is key to selection How does selection mold the existing variation? What are the similarities and differences between two separate populations? Are they due to something else besides selection?
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Fusion of chromosomes in island mice Due to chance events perhaps?
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A cline -geographic variation along an axis
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Where does this variation come from again? Mutation-ultimate source of new alleles
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Chapter 23 - Chapter 23 Evolution of populations Chapter...

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