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midterm 2 study notes

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Doug Thomson

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 b/c 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. 3. Disruptive selection- when individuals with extreme phenotypes at either end of the population distribution have higher fitness than individuals with average phenotypes. This tends to increase genetic and phenotypic variation. (though it is uncommon) • Example in textbook: industrial melanism peppered moth demonstrates genetic change in response to darkened branches to avoid predation (camoflauge) illustrates natural selection and evolutionary response over a short period of time. • Population genetics: method for predicting changes in gene frequency in response to selection (the potential for evolution exists in all populations). • Example: cactus wren has no source of water, so must avoid gaining too much heat from its environment. only live in Arizona desert. The orientation of the cactus wren changes seasonally, so the nest is facing away form the cool winds in winter, and in the summer, is facing toward the cool wind. • Reaction norm: observed relationship b/w the phenotype and the environement. Example: heat energy heat accelerates most life processes. The butterfly grow faster at high temperatures. However, different environments differ in this relationship. • Examples of acclimization: growing thicker fur, producing smaller leaves, increasing number of red blood cells, and producing enzymes that remain fluid at diff temperatures. • Process of modifying the body’s structure and metabolic machinery. (is reversible!) • However, increased tolerance to one extreme brings reduced tolerance to another. • Textbook example: creoste bush change temperature optima with seasons. Their acclimization results from changes in the viscosity of the membranes directly involved in photosynthesis. • A species capacity for acclimization may reflect the range of conditions in its environment. • Developmental responses: when the attribute of the indivudal is modified for a long time, even its whole lifetime. Example: African grasshopper change colours with response to seasons to hide from predators this change is irreversible! • Genotype-environment interaction – when a genotype performs better in one environment than the other. these relationships can be revealed by reciprocal transplant experments. • An example of the experiment: the growth rate of fence lizards reveal both genetic determination and phenotypic plasticity. When there are fewer resources, lizards cannot gather resources fast enough to support their natural growth rate (which is higher). And when, lizards have a genetically fixed slow growth rate, they cannot take advantage of more resources when put into a more abundant environment. Chapter 8 • Parthegnogenesis- reproduce asexually by forming diploid eggs. Eggs differ from one another b/c of recombination. • In another variation of Parthegnogenesis Type of self-fertilization. This method of sexual reproduction is most frequently encountered as selfing in plants. • Twofold cost of meiosis- 50% genetic cost of sexual reproduction. However, this cost does not apply when the sexes are separate b
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