 What do you know about Gregor Mendel?  Considered the Father of Genetics  Worked with Pea plants and discovered that gene inheritance follows certain patterns. ▪ Mendelian Inheritance

 Griffith was trying to figure out how bacteria make people sick.  He had isolated two different strains of bacteria that caused pneumonia. ▪ What is a strain of bacteria?  One strain made mice sick and die. The other did not.

 Griffith thought that maybe the harmful strain were producing a poison.  So Griffith killed the harmful bacteria with heat and then injected it into the mice.

 What do you think happened?

 The Mice Survived!  So Griffith then mixed the dead bacteria with live bacteria of the harmless strain and injected the mixture into the mice.  By themselves, neither should have caused the mice to die.  But the mice died.

 Somehow the heat-killed bacteria had passed on their disease-causing ability to the harmless strain.  The harmless strain was transformed.  The offspring of those once harmless bacteria also killed mice. ▪ So the harmful trait was inherited.

▪ Griffith hypothesized that when the live, harmless bacteria and heat-killed bacteria were mixed, some factor was transferred from the dead cells to the live cells. ▪ This factor changed the harmless bacteria into a harmful bacteria. ▪ But what could that factor be? ▪ What did we learn from Griffith’s experiment?

 Repeated Griffith’s experiment, but tried to figure out what molecule transformed the harmless bacteria.  They mixed the heat-killed bacteria with enzymes that destroyed different types of molecules.  Carbohydrates, proteins, RNA, and lipids The bacteria still transformed the harmless bacteria.

 When they mixed the heat-killed bacteria with a solution that destroyed the DNA molecule transformation did not occur.  What does this mean?

 DNA could be the molecule that stored and transmits genetic information that is inherited.  What did we learn from Avery’s experiment

 What animal did Frederick Griffith experiment with?  What did he inject them with?  What is a strain of bacteria?  Describe these experiments for me.  What did we learn from Griffith’s experiment?

 Who’s experiment did Oswald Avery repeat?  What did he change about that experiment?  Which molecule seemed to be linked to the transfer of genetic information by Avery’s experiment?  What did we learn from Avery’s experiment?  Please leave an Open space between Avery and the next scientists we will talk about.

 These scientists were skeptical.  They wanted to do some more tests before they could trust that DNA is what holds genetic information.  Instead of working with bacteria they worked with viruses.

 What is a virus?  Non-living particles smaller than a cell that infect living organisms.  They have a protein shell that surrounds DNA or RNA. ▪ That is basically all that they are made of. ▪ Viruses enter a cell and injects genetic information into a cell. Then the cell is gradually destroyed as it produces more viruses from that genetic information.

 They thought that if they could figure out if it was the protein coat or the DNA core that was injected into cells than they would know what exactly passed along the genes that told the cell to make more viruses.  Can someone explain why they thought this? Protein Coat

T here is sulfur in proteins There is Phosphorous in DNA Hershey and Chase did labeled some viruses with radioactive sulfur and some with radioactive phosphorous.

Then they let the Viruses do their thing. Only the genetic material would be left in the cell. What they discovered was that only the cells that were injected with viral DNA were radioactive. What does this mean?

 The genetic material injected into the cells was DNA!  What does this mean?  So, what important thing did Hershey and Chase discover?

 Why did Hershey and Chase bother?  Why not just trust Avery’s results?  Why are Scientists Skeptical?