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Unformatted text preview: 4/7/11 1 Lecture 3 Historical Overview Modern Synthesis and Selection Darwin ` s Postulates and Modern View 1. Individuals within a species are variable. 1. As a result of mutation, segregation, and independent assortment, individuals within a species are variable. Historical Overview Modern Synthesis 2. Some of these variations are passed on to offspring. 2. Individuals pass their genes on to their offspring intact and independently of other genes. Historical Overview Modern Synthesis 3. In most generations, more offspring are produced than can survive. 3. In most generations, more offspring are produced than can survive. Historical Overview Modern Synthesis 4. Survival and reproduction are not random: The individuals that survive and go on to reproduce, or who reproduce the most, are those with the most favorable variations. They are naturally selected. most favorable variations = alleles and allelic combinations that best adapt them to their environment. Historical Overview Modern Synthesis Outcome: Alleles associated with higher fitness increase in frequency from one generation to the next. Natural Selection Example - Medium Ground Finch Medium Ground Finch ( Geospiza fortis ) studied by Rosemary and Peter Grant from 1970 ` s to present seed-eating bird Darwin ` s Finch can test each of the four postulates using this species. Fig 3.6 4/7/11 2 Natural Selection - example 1. Do individuals within a species vary? All traits measured on Medium Ground Finch are variable Example: Bill Depth Fig 3.9 Natural Selection - example 2. Is this variation heritable? Parents with thick beaks tend to have offspring with thick beaks. Parents with thin beaks tend to have offspring with thin beaks....
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