16_Lecture_part1_post

16_Lecture_part1_post - The Molecular Basis of Inheritance...

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The Molecular Basis of Inheritance Overview : Life’s Operating Instructions In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA DNA, the substance of inheritance, is the most celebrated molecule of our time Hereditary information is encoded in DNA and reproduced in all cells of the body This DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits
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The Search for the Genetic Material: Scientific Inquiry When T. H. Morgan’s group showed that genes are located on chromosomes, the two components of chromosomes DNA and protein became candidates for the genetic material The key factor in determining the genetic material was choosing appropriate experimental organisms The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them
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Evidence That DNA Can Transform Bacteria The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928 Griffith worked with two strains of a bacterium, one pathogenic and one harmless When he mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became pathogenic He called this phenomenon transformation , now defined as a change in genotype and phenotype due to assimilation of foreign DNA
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Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells Mouse dies Mouse dies Mouse healthy Mouse healthy Living S cells EXPERIMENT RESULTS
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In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that the transforming substance was DNA Their conclusion was based on experimental evidence that only DNA worked in transforming harmless bacteria into pathogenic bacteria Many biologists remained skeptical, mainly because little was known about DNA
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16_Lecture_part1_post - The Molecular Basis of Inheritance...

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