Ch. 20 - Recombinant DNA Technology

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook

Klug 12th Edition

Ch. 20 - Recombinant DNA Technology

Problem 14

Chapter 20, Problem 14

What advantages do cDNA libraries provide over genomic DNA libraries? Describe cloning applications where the use of a genomic library is necessary to provide information that a cDNA library cannot.

Verified step by step guidance

Understand the nature of cDNA libraries: cDNA libraries are made from mRNA transcripts that have been reverse-transcribed into complementary DNA (cDNA). This means they represent only the expressed genes in a particular tissue or cell type at the time of RNA extraction, and they lack introns and non-coding regions.

Recognize the advantages of cDNA libraries: Since cDNA libraries contain only coding sequences (exons), they are useful for studying gene expression, producing recombinant proteins, and identifying coding sequences without introns, which simplifies cloning and expression in prokaryotic systems.

Understand the nature of genomic DNA libraries: Genomic libraries contain fragments of the entire genome, including coding regions, introns, regulatory sequences, and intergenic regions. They represent the complete genetic content of an organism.

Identify cloning applications requiring genomic libraries: When studying gene regulation, intron-exon structure, promoter regions, or non-coding DNA elements, a genomic library is necessary because cDNA libraries lack these sequences. Also, for organisms with alternative splicing or unknown gene structures, genomic libraries provide the full context.

Summarize the complementary uses: Use cDNA libraries to analyze expressed genes and produce proteins, and use genomic libraries to investigate gene structure, regulatory elements, and genomic organization that cDNA libraries cannot provide.

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Key Concepts

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

cDNA Libraries

cDNA libraries are collections of complementary DNA sequences synthesized from mRNA transcripts, representing only the expressed genes in a cell at a given time. They exclude non-coding regions like introns and regulatory sequences, making them useful for studying gene expression and producing protein-coding sequences.

Genomic DNA Libraries

Genomic DNA libraries contain fragments of an organism's entire genome, including coding regions, introns, regulatory elements, and intergenic sequences. They provide a comprehensive representation of all genetic material, which is essential for studying gene structure, regulatory sequences, and non-expressed regions.

Applications Requiring Genomic Libraries

Genomic libraries are necessary when information about gene regulation, intron-exon structure, or non-coding DNA is required. They are crucial for cloning entire genes with regulatory elements, studying mutations in non-coding regions, or analyzing genome organization, which cDNA libraries cannot provide due to their focus on expressed sequences only.

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Related Practice

Textbook Question

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

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Textbook Question

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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Textbook Question

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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Textbook Question

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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Textbook Question

To create a cDNA library, cDNA can be inserted into vectors and cloned. In the analysis of cDNA clones, it is often difficult to find clones that are full length—that is, many clones are shorter than the mature mRNA molecules from which they are derived. Why is this so?

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Textbook Question

Although the capture and trading of great apes has been banned in 112 countries since 1973, it is estimated that about 1000 chimpanzees are removed annually from Africa and smuggled into Europe, the United States, and Japan. This illegal trade is often disguised by simulating births in captivity. Until recently, genetic identity tests to uncover these illegal activities were not used because of the lack of highly polymorphic markers (markers that vary from one individual to the next) and the difficulties of obtaining chimpanzee blood samples. A study was reported in which DNA samples were extracted from freshly plucked chimpanzee hair roots and used as templates for PCR. The primers used in these studies flank highly polymorphic sites in human DNA that result from variable numbers of tandem nucleotide repeats. Several offspring and their putative parents were tested to determine whether the offspring were 'legitimate' or the product of illegal trading. The data are shown in the following Southern blot.

Examine the data carefully and choose the best conclusion.

a. None of the offspring is legitimate.

b. Offspring B and C are not the products of these parents and were probably purchased on the illegal market. The data are consistent with offspring A being legitimate.

c. Offspring A and B are products of the parents shown, but C is not and was therefore probably purchased on the illegal market.

d. There are not enough data to draw any conclusions. Additional polymorphic sites should be examined.

e. No conclusion can be drawn because 'human' primers were used.

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