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Ch. 20 - Recombinant DNA Technology
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All textbooksKlug 12th EditionCh. 20 - Recombinant DNA TechnologyProblem 17

Chapter 19, Problem 17

Variable number tandem repeats (VNTRs) are repeating DNA sequences of about 15–100 bp in length, found both within and between genes. Why are they commonly used in forensics?

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Welcome back. Here's our next problem. It says blank are sequences with repeating units ranging in length from 7-100 base pairs. Whereas blank have repeating units with a length of 1-6 base pairs. And when we look over our answer choices we see we kind of have three terms that are mixed up in different orders as our different choices short tandem repeats, satellite D. N. A. And variable number tandem repeats. Well these repeating units um in the sequences that has said we have choices between 1-6 base pairs or 7-100 base pairs are called Tandem repeats. And there are two types of them. And these tandem repeats of DNA sequences have these two types variable length, sometimes abbreviation abbreviated Vien tr, variable number tandem repeats between seven and 100 base pairs and then short tandem repeats sTR. Of 1 to 6 base pairs. So with that in mind we can look for answer choice. We know the first blank 7 100 must be the variable number tandem repeats. So we see that choice b. And choice d have that as their first term. And so we can eliminate choice A. And Choice C. Has short tandem repeats. First C. Has satellite D. N. A. And then we want our second space to be short tandem repeats and we find that in choice B. But not choice D. So we know that choice B is our correct answer and choice D. Can be eliminated. We C. We also that term satellite D. N. A. And satellite D. N. A. Consists of D. N. A sequences including several thousands of base pairs of very repetitive DNA. So just huge segments of very repetitive D. N. A. And it's the main component of hetero chroma tin, that densely packed form of protein that has very few genes and is not transcribed. So that's what satellite D. N. A. Is. And it's not one of these two things. So Choice B. Variable number tandem repeats are sequences with repeating units from 7 to 100 base pairs, whereas short tandem repeats have repeating units of 1 to 6 base pairs. See you in the next video.
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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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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 are 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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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  phage DNA contains approximately 48,500 bp, how many cleavage sites would you expect?

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