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Transcript
Evolution: An Introduction A Scientific Theory • Must make predictions. • Must be in agreement with the evidence and be the best explanatory model. • Must be verifiable – potentially falsifiable (capable of being tested). A Scientific Theory is NOT “flawed” or invalid when… • It cannot account for an observation • It is incomplete • A particular piece of evidence cannot be found ALL Scientific Theories are Incomplete What is the Theory of Evolution? • Evolution is the process in which significant changes to genetic traits of a species occur over successive generations i.e. any shift in the gene pool of a population End Result: • The adaptation of a species to its environment • Individuals cannot evolve – populations are the smallest unit that can evolve What Drives Evolution? (1) Mutations – Mutations are not related to the present needs of an organism but are merely the result of chance. (2) Sexual Reproduction – Results in recombination of 1000s of different alleles – E.g. an individual of a species with 20 000 genes that is heterozygous at only 10% of these loci could produce 220000 different allelic recombination in their gametes Somatic Mutation • Happens in a body cell (e.g. skin and stomach cells) • Are the cause of some cancers • Not passed on to the next generation Germ-like Mutation • Occurs in the cells that give rise to gametes (sperm and egg cells) • Are heritable (which means that they can be passed on to the offspring) Are all mutations harmful? Why or Why not? • Not all mutations are harmful • Some are beneficial by providing a selective advantage (i.e. organism is favoured in terms of survival and reproduction) • Other mutations are neutral – no effect on organism’s fitness (ability to reproduce), but may become critical for survival later if the environment changes Why are harmful mutations not passed on to the next generation? • Most harmful mutations typically reduce an organism’s fitness and don’t live long enough to pass on their traits Seatwork Read and answer Bed Bugs Article