Lecture 9 Chapter 7 - Introduction to Genetic Analysis...

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    1 Introduction to Genetic Analysis Ninth Edition Anthony J. F. Griffiths, Susan R. Wessler, Richard C. Lewontin,  and Sean B. Carroll CHAPTER 7 DNA: Structure and Replication Copyright 2008 © W H Freeman and Company
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    2 After Mendel before April 1953… Genes - hereditary ‘factors’ determining specific traits. Their physical and chemical nature was not understood Mutations - alter gene function and generate new alleles.  The mechanism and nature of mutation was not understood One-gene-one-protein hypothesis suggested gene function is mediated through proteins. Genes were known to be located on chromosomes. Chromosomes were known to consist of DNA and protein. It was not clear whether genetic material was protein or DNA.
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    3 The Double Helix In April 1953 James Watson and Francis Crick proposed a  model for the structure of DNA.   Their Model  Accommodated all of key properties of DNA . Defined genes in chemical terms. Paved the way for understanding at the molecular level gene - function  gene - role in heredity
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    4 Evidence that led to the discovery DNA is the transforming principle
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    5 Evidence that led to the discovery  1.  Frederick Griffith  Experiment-transforming principle The ability of a virulent strain of  Streptococcus pneumoniae..   to kill a host mouse… was transferable to a non-virulent strain.
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    6 Evidence that led to the discovery  2.  Avery, MacLeod and McCarty Experiment Polysaccharides, proteins, fats and RNA ruled out as  the transforming agent. 
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    7 Evidence that led to the discovery  2.  Hershey and Chase Genetic material of bacteriophage T2 is DNA and  not protein.
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    8 Solving a three-dimensional puzzle DNA structure must accommodate the three key properties  of DNA 1. Ability to faithfully self replicate. 1. Ability to encode heritable traits.  1. Ability to generate alternate alleles that slightly alter the  traits.  
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    9 FUNDAMENTAL PROPERTIES OF  DNA Self-Replication. Encode hereditable traits. Mutation
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    10 Three key facts from previous  discoveries or work. 1. The chemical nature of DNA, 1. Chargaff’s rules of base composition. 1. X-ray diffraction analysis of DNA from  Rosalind Franklin   and Maurice Wilkins.
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    11 Chemical nature of DNA DNA is made of three components. 1. Phosphate 1. Sugar – Deoxyribose 1. Four Nitrogen bases  1.
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