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study guide for term test 2

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Jean Jiang Nash

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Chapter 6 Inspiration to Charles Darwin: Galapagos archipelago, noticed that many organisms living in the archipelago had different forms on different islands. Original colonists: from South America The archipelago is relatively dry. The el Nino brought increased rainfall and increased vegetation, and the La nina brought drought again. The environment influences phenotypes, not genotypes. Phenotypic plascticity: the capacity of an individual to exhibit diff responses to its environment. Alleles are different forms of a particular gene. Pleiotropy- effects of a single gene on multiple traits (ex: daf-2 in worms) Many phenotypic traits show continuous variation (bell curve) like height. The process of evolution has three main ingredients: variation among individuals, inheritance of that variation, and differences in survival and reproductive success related to that variation (fitness) Example in text: California citrus pest some individuals in the pop. had alleles endowing cyanide resistances, and when the pests were first sprayed with cyanide, the organisms that did not have cyanide-resitant alleles, dies, but eventually the population of those individuals who were cyanide-resitant increased, and so in turn cyanide became useless after a while. Sometimes the environment can influence phenotypes directly, and bring changes in an individual that improves its relationship with the environment. This is referred to as acclimatization- meaning the changes are beneficial but they are not adaptations. Example in textbook: adapted the presence of a parastoid fly bc of choosy females. Selection can influence the distribution of traits in a pop in 3 ways: 1. stabilizing selection- when individuals with average phenotypes have a higher reproductive success than those with extreme phenotypes. 2. Directional selection- when the fittest individuals have an extreme phenotype this shifts the distribution of phenotypes toward a new optimum, then it is stabilized.
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