Skip to main content
Pearson+ LogoPearson+ Logo
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 16

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?

Verified step by step guidance
1
Understand the process of creating a cDNA library: cDNA is synthesized from mRNA using reverse transcriptase.
Recognize that reverse transcriptase can sometimes fall off the mRNA template before the entire mRNA is copied, leading to incomplete cDNA synthesis.
Consider the role of mRNA degradation: mRNA molecules can be partially degraded before reverse transcription, resulting in shorter cDNA.
Acknowledge that the efficiency of the reverse transcription process can vary, affecting the length of the cDNA produced.
Note that the cloning process itself can introduce biases, where shorter cDNA fragments are more easily cloned than longer ones.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2m
Was this helpful?

Key Concepts

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

cDNA Synthesis

cDNA, or complementary DNA, is synthesized from mRNA through the action of the enzyme reverse transcriptase. This process involves the reverse transcription of mRNA into a DNA strand, which can then be amplified and cloned. However, during this synthesis, incomplete reverse transcription can occur, leading to shorter cDNA fragments that do not represent the full length of the original mRNA.
Recommended video:
Guided course
02:43
Translesion Synthesis

Introns and Exons

Eukaryotic genes are composed of exons (coding regions) and introns (non-coding regions). During mRNA processing, introns are removed, and exons are spliced together to form mature mRNA. When creating a cDNA library, if the cDNA is derived from pre-mRNA or if splicing errors occur, the resulting cDNA may lack some exons, resulting in shorter clones that do not fully represent the mature mRNA.
Recommended video:
Guided course
08:39
mRNA Processing

Cloning Efficiency

The efficiency of cloning cDNA into vectors can vary based on several factors, including the quality of the cDNA, the vector system used, and the transformation process. Some cDNA fragments may be preferentially amplified or selected during cloning, leading to a bias towards shorter clones. This can make it challenging to isolate full-length cDNA clones, as they may be outcompeted by shorter, more easily cloned fragments.
Recommended video:
Guided course
07:
Positional Cloning
Related Practice
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.

613
views
Textbook Question

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.

1242
views
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.

735
views
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.

565
views
Textbook Question

To estimate the number of cleavage sites in a particular piece of DNA with a known size, you can apply the formula N/4ⁿ where N is the number of base pairs in the target DNA and n is the number of bases in the recognition sequence of the restriction enzyme. If the recognition sequence for BamHI is GGATCC and the λ\lambda phage DNA contains approximately 48,500 bp, how many cleavage sites would you expect?

1172
views
Textbook Question

In a typical PCR reaction, describe what is happening in stages occurring at temperature ranges

(a) 92-26 °C

(b) 45-65 °C and

(c) 65-75 °C

667
views