Lecture_12 - Lecture 12 - 1 I. Natural Selection...

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Lecture 12 - 1 I. Natural Selection Hardy-Weinberg and Evolution If you remember in the first few lectures, I talked about how in the late 18th century the concept of heredity was one of blending inheritance. Thus the offspring of a mating was expected (or thought) to be intermediate between two parents. Example: In a population of plants, there are tall and short individuals - if mating is at random and there is blending inheritance then: most of the population are intermediate and will cross most often producing more intermediates only way to maintain the extreme phenotypes is for them to mate with each other - otherwise the extreme phenotypes are 'blended away' BUT - we've seen with Mendelian genetics that crosses of intermediates (if these are the heterozygotes) 'recreate' the extreme phenotypes AND Hardy-Weinberg equilibrium predicts that the variation within a population will be maintained - the genotype frequencies do not change between generations This revolutionized attitudes towards evolution by natural selection - because the idea of blending inheritance was a huge stumbling block to Darwin's idea. What was Darwin's idea? 1. Variation exists among individuals for traits 2. Offspring resemble their parents more than other individuals 3. Individuals with particular forms of traits are more likely to survive and reproduce than other individuals
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Lecture_12 - Lecture 12 - 1 I. Natural Selection...

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