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Ch. 20 - Recombinant DNA Technology
Klug - Concepts of Genetics  12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
Chapter 20, Problem 12

If you performed a PCR experiment starting with only one copy of double-stranded DNA, approximately how many DNA molecules would be present in the reaction tube after 15 cycles of amplification?

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Understand that PCR (Polymerase Chain Reaction) amplifies DNA by doubling the number of DNA molecules each cycle, assuming 100% efficiency.
Identify the initial number of DNA molecules, which in this case is 1 double-stranded DNA molecule.
Recognize that after each cycle, the number of DNA molecules doubles, so the number of molecules after n cycles is given by the formula: \(N = N_0 \times 2^n\), where \(N_0\) is the initial number of molecules and \(n\) is the number of cycles.
Substitute the given values into the formula: \(N_0 = 1\) and \(n = 15\), so the expression becomes \(N = 1 \times 2^{15}\).
Calculate the value of \$2^{15}$ to find the approximate number of DNA molecules after 15 cycles.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polymerase Chain Reaction (PCR) Process

PCR is a technique used to amplify specific DNA sequences exponentially by cycling through denaturation, annealing, and extension steps. Each cycle ideally doubles the number of DNA molecules, allowing for rapid multiplication from a small initial amount.
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Exponential Amplification

In PCR, the number of DNA molecules doubles with each cycle, leading to exponential growth. Starting with one DNA molecule, after n cycles, the number of molecules is approximately 2^n, assuming 100% efficiency.

Initial Template Quantity and Cycle Number

The starting amount of DNA and the number of PCR cycles determine the final quantity of DNA. Beginning with a single double-stranded DNA molecule and performing 15 cycles results in roughly 2^15 DNA molecules, illustrating the power of PCR amplification.
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What are the advantages of using a restriction enzyme whose recognition site is relatively rare? When would you use such enzymes?

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In 1975, the Asilomar Conference on Recombinant DNA was organized by Paul Berg, a pioneer of recombinant DNA technology, at a conference center at Asilomar State Beach in California. Physicians, scientists, lawyers, ethicists, and others gathered to draft guidelines for safe applications of recombinant DNA technology. These general guidelines were adopted by the federal government and are still in practice today. Consider the implications of recombinant DNA as a new technology. What concerns might the scientific community have had then about recombinant DNA technology? Might those same concerns exist today?

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In the context of recombinant DNA technology, of what use is a probe?

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In a control experiment, a plasmid containing a HindIII recognition sequence within a kanamycin resistance gene is cut with HindIII, re-ligated, and used to transform E. coli K12 cells. Kanamycin-resistant colonies are selected, and plasmid DNA from these colonies is subjected to electrophoresis. Most of the colonies contain plasmids that produce single bands that migrate at the same rate as the original intact plasmid. A few colonies, however, produce two bands, one of original size and one that migrates much less far down the gel. Diagram the origin of this slow band as a product of ligation.

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You have recovered a cloned DNA segment from a vector and determine that the insert is 1300 bp in length. To characterize this cloned segment, you isolate the insert and decide to construct a restriction map. Using enzyme I and enzyme II, followed by gel electrophoresis, you determine the number and size of the fragments produced by enzymes I and II alone and in combination, as recorded in the following table. Construct a restriction map from these data, showing the positions of the restriction-enzyme cutting sites relative to one another and the distance between them in units of base pairs.

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