lecture%204%20natural%20selection%20A - 10/6/09 Why are...

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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
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lecture%204%20natural%20selection%20A - 10/6/09 Why are...

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