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PDF_notes_Mechs 2 - Mechanisms of Evolution 2 Genetics D2L...

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Mechanisms of Evolution 2: Genetics D2L quiz closes Feb 5
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Today’s Outline • Blending vs. discrete inheritance • Genotype and phenotype • Two approaches to evolutionary genetics • How natural selection causes adaptation • Other factors in evolution
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A Problem with Darwin’s original theory: • Natural selection is variation, selection, inheritance • Through blending, variation is lost too quickly • Blending inheritance : offspring are the average of their parents
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But Darwin didn’t know that: • Phenotypes appear to blend when influenced by many different genes, but actually the units of inheritance (genes) don’t blend; they are passed on as discrete (all-or-nothing) units. • New combinations of genes in each generation produce new phenotypic variation in each generation. • This was shown by Mendel, hence is called Mendelian genetics
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Discrete Mendelian genes AA aa AA aa AA aa AA aa AA aa AA aa Aa Aa Aa Aa AA aa AA aa Aa Aa Aa Aa This stability = Hardy-Weinberg equilibrium
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• An individual’s genotype consists of its genes. • An individual’s phenotype consists of its traits.
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The relationship between genotype and phenotype isn’t always simple • Different genotypes can produce the same phenotype – Dominance: AA and Aa genotypes have same phenotype • Different phenotypes can result from the same genotype – Phenotype is also influenced by environment.
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Relationship between genotype and phenotype isn’t always simple • Phenotypic plasticity : : same genotype produces different phenotypes in different environments – E.g., limpets grow different shape when exposed to waves.
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Genes, alleles and polymorphism •Genes are found at specific locations on chromosomes:
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This note was uploaded on 01/31/2009 for the course BIO 182 taught by Professor Chaux during the Spring '08 term at Arizona.

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PDF_notes_Mechs 2 - Mechanisms of Evolution 2 Genetics D2L...

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