lecture2 - Natural Selection 22 and 24 June Natural...

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Natural Selection 22 and 2 4 June 1 Natural selection – a process that produces adaptations resulting from differential reproductive success among organisms in the same population Adaptations – characteristics (traits) that suit organisms to their environment Reproductive success – number of viable offspring produced during an organism’s entire life Fitness – reproductive success of an organism relative to others in the same population Conditions necessary for natural selection Conditions necessary for natural selection 1. Variation in traits among organisms exists – phenotypic variation Frequency Trait (size) 2. Different phenotypes have different fitnesses Frequency Yellow Green 3. Phenotypic variation is heritable (i.e. variation has a genetic component) Genotypes Traits Fitness
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Natural Selection 2 2 and 2 4 June 2 Types of Natural Selection Types of Natural Selection Frequency Trait (size) Stabilizing Before After Variance decreases Directional Disruptive Distribution shifts Variance increases Frequency- dependent Industrial Melanism in Peppered Moths Industrial Melanism in Peppered Moths Before 1850. Nearly all moths were typical and blended in with lichens on tree trunks. 1850-1900. Pollution near industrial areas killed lichens on trees, carbonaria moths blended in with the dark bark on trees and their frequency increased. 1900-1950. In polluted areas most moths were carbonaria, whereas in unpolluted areas most moths were typical . What caused the change in phenotypic frequencies in polluted are What caused the change in phenotypic frequencies in polluted are as? as? Kettlewell Kettlewell ’s hypothesis: bird predation s hypothesis: bird predation
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Natural Selection 2 2 and 2 4 June 3 Typical Typical moths became more common in moths became more common in industrial areas as pollution decreased carbonaria
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Natural Selection 2 2 and 2 4 June 4 Resistance to Chemical Pesticides by Insects Resistance to Chemical Pesticides by Insects Heavy Metal Tolerance in Plants Heavy Metal Tolerance in Plants In <50 years the grass Agrostis tenuis evolved populations that live on mine wastes in Great Britain. Normal populations of A. tenuis contain a few (<0.1%) tolerant genotypes. In normal soil, tolerant genotypes are poorer competitors compared to non- tolerant genotypes. In California, Mimulus nudatus is restricted to serpentine soils, whereas M.
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This note was uploaded on 01/06/2010 for the course EVE 101 taught by Professor Strong,d during the Spring '08 term at UC Davis.

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lecture2 - Natural Selection 22 and 24 June Natural...

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