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Natural Selection.docx

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Western University
Biology 1201A
Tom Haffie

Natural Selection 17.3, 16.1, 16.3d, 16.5 Charles Darwin (1809-1882) - 1831 – travels on HMS Beagle - Contributors o Lyell’s Principle of Geology book o Malthus’s Essay on the Principles of Population  Competition for resources - Galapagos Islands – why so many diff. organisms occupy one small island cluster? - Artificial Selection o Selective breeding of animals/plants to ensure that certain desirable traits appear at higher frequency in successive generations - Natural Selection o Evolutionary process by which alleles that increase the likelihood of survival and the reproduction output of the individuals that carry them become more common in subsequent generations - On the Origins of Species o Descent w/ modification  Evolutionary alteration and diversification of ancestral species Variation in Natural Population - Phenotypic Variation o Differences in appearance/function – that if based on heritability – are passed from generation to generation o Possibilities  Different genotype exhibit same phenotype  Same genotype exhibit different phenotype o In population, cause by: 1) genetic difference 2) environmental factors 3) genetics & enviro.  Only genetically based variation is subject to evolutionary change o Quantitative Variation  Individuals differ in small, incremental ways  E.g. mass, toe length of students in biology  Bar Graphs  Describe Population o Variability  Broad, low curve – a lot of variation  High, narrow – little variation o Mean  average value of character o Qualitative Variation  2 or more discrete states, NO intermediate form  E.g. geese are either blue or white o Polymorphism  Discrete variants of a character  E.g. type A, B, AB, O, number of stripes, background colour - Genetic Variation o Sources  Production of new alleles  Rearrangement of existing alleles o Measuring  Gel Electrophoresis  Seperates 2 or more forms of a given protein if they differ significantly in shape, mass, or net electrical charge o Identifying protein infer genetic variation at the locus coding for that pro
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