outline 18-Sources of genetic variation

outline 18-Sources of genetic variation - BSCI106 Dr. Via...

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BSCI106 Outline 18 Fall, 2008 Dr. Via Sources of genetic variation The phenotype is more than the genotype Most characters influenced by several loci Multiple environmental effects Food, Water, Temperature, etc. Phenotypic variation = genetic var. at all loci + variation due to all environmental effects Only genetic variation influences evolution! Offspring DO NOT inherit characteristics caused by the environment! Example: 1909 Johannssen Grew one genotype of plant in different environments Small seeds large seeds (av = 27.8 g) (av = 42.8 g) progeny 36.6g 37.5 g progeny Sources of Genetic Variation Segregation- circle segregation on this figure b breaks up new combinations of maternal and paternal alleles Independent assortment Leads to new combinations of genes on different chromosomes– important when Traits are polygenic There is epistasis 2 n chromosome combinations! Recombination (crossing over) Occurs right after tetrad formation Produces new allele combinations on same homolog Can produce duplicated genes (unequal crossover) or new genes Can get crossover on each chromatid (double crossover) Result: 2 or 4 hybrid chromosomes!
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BSCI106 Outline 18 Fall, 2008 Dr. Via Meiosis is Complex! Why have sex and meiosis? Why aren’t all organisms asexual?? Having genetically variable progeny is advantageous Won’t all get the same disease (especially important in plants) Some will survive and reproduce if conditions change Sources of Genetic Variation
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outline 18-Sources of genetic variation - BSCI106 Dr. Via...

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