1. Horizontal gene transfer - principles
2. Transformation and transduction
3. Conjugation

1. The concepts covered here can be reviewed in your textbook, pages 232-235, and your lecture notes.

2. Transformation involves the uptake of DNA fragments (or plasmids) from the environment. The cell that uptakes the DNA is the recipient? What happens to the donor cell?

3. The study of transformation was instrumental in showing that DNA is the carrier of genetic information in living cells. Review from your textbook and notes the experiment performed by Griffiths with Streptococcus pneumoniae. This experiment consisted of four treatments, of which three can be considered "controls" and one provided evidence for transformation. Below are the four treatments:

• Living encapsulated strain
• Living non-encapsulated strain
• Dead (autoclaved) encapsulated strain
• Living non-encapsulated strain + dead (autoclaved) encapsulated strain

Copy them in your study books and for each one answer the following:

• Was this a "control" or a "transformation" treatment?
• What was the expected outcome for the animal?
• What was the observed outcome from the animal?
• What was the expected outcome when trying to isolate pathogen from treated animal?
• What was the observed outcome when trying to isolate pathogen from treated animal?
• Did expected and observed outcomes match? If NO, what is the explanation?

4. With his experiment, Griffiths demonstrated that a chemical from virulent S. pneumoniae can transform non-virulent S. pneumoniae. Can you think of (and describe) an experiment that attempts to answer the question exactly which chemical is responsible for the transformation?

5. In transduction, a virus transfers genetic material from one bacterium to another. On a piece of paper, write down the definitions of the two types of transduction - generalized and specialized.

6. Study your notes and figure 8.29 from your textbook. Then, on a piece of paper, draw your own diagram that shows how generalized transduction occurs (don't worry about making the viruses, cells, etc. well drawn, rather make sure to get the main concepts and steps of the process). Make sure to compare your diagram to the textbook figure.

7. If you feel that you have mastered the concepts on this page, you can move to the next topic of this sub-unit, which explores the transfer of plasmids via conjugation.