Natural Selection

Natural Selection - Why are some traits considered vestigial Lecture 4 Natural Selection Reading Text Ch 23 a They improve the fitness of an

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10/6/09 1 Lecture 4 Natural Selection Reading Text Ch. 23 Why are some traits considered vestigial? a. They improve the fitness of an individual who bears them, compared with the fitness of individuals without them. b. They change in response to environmental influences. c. They existed a long time in the past d. they are reduced in size, complexity, and function compared with traits in related species Overview I. Background II. Artificial selection III. Variation IV. Measuring natural selection V. Different modes of selection GRAPHING short long Human leg length Human arm length short long Human arm length and leg length are positively related The intensity of light decreases as water depth increases Y X Y X shallow deep Water depth Relative light intensity low high GRAPHING short long Human leg length Y X Y X shallow deep Water depth X and Y axes – both dependent variables X axis – independent variable Y axis – dependent variable independent variable – always on X axis GRAPHING Frequency histogram Height of each bar – frequency of each observation
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10/6/09 2 Phenotype - the characteristics of an organism, due to both genes and the environment Genotype - genetic composition of an organism Willow ptarmigan ( Lagopus lagopus ) Each individual molts with change of season summer winter Phenotypes Snow geese ( Chen caerulescens ) white and “blue” forms Color caused by single gene Genotypes Human height Different phenotypes or genotypes? Natural selection - differential survival and reproduction of phenotypes Fitness - contribution an individual makes to the gene pool of the next generation, relative to the contribution of other individuals Adaptation – heritable trait that increases fitness of an individual, relative to others Acclimatization – when an individual changes in response to environmental conditions
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10/6/09 3 “Survival of the fittest” II. Artificial selection Artificial selection - natural selection imposed by humans for a specific goal, as in the breeding of crops, animals Rock Pigeon English Carrier pigeon Pouter pigeon Fantail pigeon Many spectacular examples of artificial selection Brussels sprouts broccoli cauliflower kohlrabi kale Wild cabbage (common ancestor) Brassica oleracea cabbage How did cauliflower come to be? How did cauliflower come to be? 1. individuals vary 2. individuals with certain traits - greater survival/reproduction (selection) 3. variation is heritable (genetic) 4. result- evolution
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10/6/09 4 III. Variation – where does it come from? 1. MUTATION *change in genetic material of an organism *only source of NEW genetic variation Can be anything from point mutations (substitution of one nucleotide for another) to the duplication of entire genomes Due to copying errors during cell division mutagens - chemicals, radiation III. Variation – where does it come from? 2. SEXUAL RECOMBINATION
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This note was uploaded on 12/02/2009 for the course BILD BILD 3 taught by Professor Woodruff during the Fall '08 term at UCSD.

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Natural Selection - Why are some traits considered vestigial Lecture 4 Natural Selection Reading Text Ch 23 a They improve the fitness of an

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