1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu discovered harmless bacteria turn virulent when mixed with disease causing bacteria.  A bacteria that is virulent is able to cause disease.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu  Griffith discovered what is now called transformation - a change in genotype when cells take up foreign genetic material.

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Avery’s Experiments  In 1944, the material responsible for transformation is not affected by protein- destroying 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.

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu http://www.cellsalive.com/phage.htm

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu  The injected DNA molecules causes the bacterial cells to produce more viral DNA and proteins.

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu http://www.pbs.org/wgbh/nova/sciencenow/3411/02.htmlwww.pbs.org/wgbh/nova/sciencenow/3411/02.html How does environment affect your DNA?