Understanding 28.pdf - Understanding 28 In an elegant...

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Understanding 28. In an elegant experiment the results are so clear that conclusions can be easily made from them. Explain which specific details from Meselson’s and Stahl’s results are the best evidence that DNA is replicated semi-conservatively. Generation 0 DNA isolated from cells at the start if the experiment (before the switch to nitrogen medium) produced a single band after centrifugation. This result made sense because the DNA should have contained only heavy nitrogen at that time. Generation 1 DNA isolated after one generation (one round of DNA replication) also produced a single band when centrifuges. However, this band was higher, intermediate in density between heavy nitrogen DNA and light nitrogen DNA. The intermediate band told Meselson and Stahlt that the DNA molecules made in the first round of replication were a hybrid of light and heavy DNA. THis result fit with the dispersive and semi-conservative models, but not with the conservative model.

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