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Identifying the Genetic Material Relate Griffith’s conclusions to the observations he made during the transformation experiments. Summarize the steps involved in Avery’s transformation experiments, and state the results. Evaluate the results of the Hershey and Chase experiment. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Griffith’s Experiments In 1928, Frederick Griffith, a bacteriologist, trying to make a vaccine against pneumonia. A vaccine is prepared from killed or weakened disease-causing agents, including bacteria. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. discovered harmless bacteria turn virulent when mixed with disease causing bacteria. A bacteria that is virulent is able to cause disease. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Griffith discovered what is now called transformation a change in genotype when cells take up foreign genetic material. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Avery’s Experiments In 1944, the material responsible for transformation is not affected by proteindestroying enzymes. The activity is stopped, however, by a DNA-destroying enzyme. 100 years after Mendel’s experiments, Avery demonstrated that DNA is the material responsible for transformation. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. DNA’s Role Revealed In 1952, Alfred Hershey and Martha Chase used the bacteriophage T2 to prove that DNA carried genetic material. A bacteriophage, is a virus that infects bacteria. When phages infect bacterial cells, the phages are able to produce more viruses, which are released when the bacterial cells rupture. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. http://www.cellsalive.com/phage.htm Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. DNA’s Role Revealed • Hershey and Chase concluded that the DNA of viruses is injected into the bacterial cells, while most of the viral proteins remain outside. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. The injected DNA molecules causes the bacterial cells to produce more viral DNA and proteins. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. How does environment affect your DNA? http://www.pbs.org/wgbh/nova/sciencenow/3411/02.html Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.