Sample student results, Student Sheet 8.1, “Investigating DNA Replication”

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Science and Global Issues (SGI) Genetics: Feeding the World Matthew Meselson and Franklin Stahl’s Experiment to Investigate DNA Replication

First: Scientists James Watson and Francis Crick propose a method of semi-conservative replication in their paper on the structure of DNA. However, they have no data to support their hypothesis.

Next: Matthew Meselson and Franklin Stahl use the procedure that follows to investigate DNA created by the process of DNA Replication. Procedure 1. Place bacteria, Escherichia coli (E. coli) in a solution of “heavy” nitrogen.

2. Leave the E. coli in the “heavy” nitrogen solution until all DNA nucleotides, and all DNA strands, are made of “heavy” nitrogen. This is Generation Zero.

3. Isolate the DNA from the E. coli.

4. Place “heavy” DNA in a solution with the same density as DNA.

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Science and Global Issues (SGI) Genetics: Feeding the World 5. Run “heavy” DNA solution on a centrifuge. A band of “heavy” DNA forms in the test tube.

6. Transfer some of the E. coli with “heavy” DNA into a solution of “light” DNA.

7. Allow the E. coli to reproduce for 20 minutes (the reproduction time of E. coli).

8. Place E. coli in the solution and run the tube on a centrifuge.

9. Analyze the bands of DNA that form.

10. Repeat for 3 rounds of Replication.

11. Compare the bands that form for each round of replication.

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Meiosis

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Science and Global Issues (SGI) Genetics: Feeding the World