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Thinking Scientifically
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1. To diagnose a rare form of encephalitis (brain inflammation), a researcher needs a million copies of a viral gene. She decides to use the polymerase chain reaction on a sample of cerebrospinal fluid, which bathes the person’s infected brain. If one cycle of PCR takes 2 minutes, how long will it take the researcher to obtain her million-fold amplification starting with a single copy?

2. Give an example from the chapter of when different types of experiments were used to address the same hypothesis. Why might this be necessary?

3. The experiments that revealed DNA structure and function used a variety of organisms. How can such diverse organisms demonstrate the same genetic principles?

4. A person with deficient or abnormal ligase or excision repair may have an increased cancer risk and chromosomes that cannot heal breaks. The person is nevertheless, alive. How long would an individual lacking DNA polymerase be likely to survive?

5. HIV infection was once diagnosed by detecting antibodies in a person’s blood or documenting a decline in the number of the type of white blood cell that HIV initially infects. Why is detection using PCR more accurate?


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Additional Questions and Terms

1. Cancerous cells from a person with hereditary nonpolyposis colon cancer have different length microsatellite sequences. What is the nature of the defect in DNA repair underlying the cancer?

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