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Ch. 12 - DNA Organization in Chromosomes
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All textbooksKlug 12th EditionCh. 12 - DNA Organization in ChromosomesProblem 30

Chapter 12, Problem 30

Because of its rapid turnaround time, fluorescent in situ hybridization (FISH) is commonly used in hospitals and laboratories as an aneuploid screen of cells retrieved from amniocentesis and chorionic villus sampling (CVS). Chromosomes 13, 18, 21, X, and Y (see Chapter 8) are typically screened for aneuploidy in this way. Explain how FISH might be accomplished using amniotic or CVS samples and why the above chromosomes have been chosen for screening.

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Hi everyone. Let's look at our next question. It says what is the significance of fluorescence in C. Two hybridization or F. I. S. H. In investigating chromosomes, let's recall what this technique is. You kind of have a key from the name here. But it's a technique in which a specific DNA sequence can be detected and located in a chromosome using a primer tag the fluorescence. I have a primer that's complementary to the sequence you're looking for. And that primer has a fluorescent tag on it. So with that in mind let's look through our answer choices here, noting that we're looking for the significance of this in investigating chromosomes. Choice A says it is used to artificially synthesized DNA. Well that is not correct. Just locates a sequence. Makes a small primer that binds to a complementary sequence. Doesn't synthesize DNA. Choice B says it records cell division. Well this would not be the main purpose of it. Uh Scientists use a stain to stain the different to stain the chromosomes and see visually see their progress through cell division choice C says it detects and locates a specific DNA sequence. And this is our answer choice. As we said, the valuable um aspect of it is that it can find with this florescent tag and its specificity a specific DNA sequence among all the chromosomes. So you can see the physical location of a gene on a chromosome with this technique it doesn't even have to be a whole gene. It can be just a particular sequence and then finally Choice. D. Says it determines the exact length of the whole genome. And that's not correct. Since it just binds to this one D. N. A sequence that isn't what you'd use it for. If you want to determine the length of the whole genome, you would actually look for the mass of D. N. A. In the nucleus which you could then use um the you could convert to the number of base pairs in that genome just by looking at the mass of D. N. A. And the nucleus. So again, what is the significance of fluorescence and see two hybridization or F. I. S. H. In investigating chromosomes? And that's choice C. It detects and locates a specific DNA sequence in the next video?
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An article entitled 'Nucleosome Positioning at the Replication Fork' states: 'both the 'old' randomly segregated nucleosomes as well as the 'new' assembled histone octamers rapidly position themselves (within seconds) on the newly replicated DNA strands' [Lucchini et al. (2002)]. Given this statement, how would one compare the distribution of nucleosomes and DNA in newly replicated chromatin? How could one experimentally test the distribution of nucleosomes on newly replicated chromosomes?
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Spermatogenesis in mammals results in sperm that have a nucleus that is 40 times smaller than an average somatic cell. Thus, the sperm haploid genome must be packaged very tightly, yet in a way that is reversible after fertilization. This sperm-specific DNA compaction is due to a nucleosome-to-nucleoprotamine transition, where the histone-based nucleosomes are removed and replaced with arginine-rich protamine proteins that facilitate a tighter packaging of DNA. In 2013 Montellier et al. showed that replacement of the H2B protein in the nucleosomes with a testis-specific variant of H2B called TSH2B is a critical step prior to the nucleosome-to-nucleoprotamine transition. Mice lacking TSH2B retain H2B and their sperm arrest late in spermatogenesis with reduced DNA compaction. Based on these findings, would you expect that TSH2B-containing nucleosomes are more or less stable than H2B-containing nucleosomes? Explain your reasoning.
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To gauge the fidelity of DNA synthesis, Arthur Kornberg and colleagues devised a technique called nearest-neighbor analysis, which determines the frequency with which any two bases occur adjacent to each other along the polynucleotide chain (J. Biol. Chem. 236: 864–875). This test relies on the enzyme spleen phosphodiesterase (see the previous problem). As we saw in Figure 11-8, DNA is synthesized by polymerization of 5'-nucleotides—that is, each nucleotide is added with the phosphate on the of deoxyribose. However, as shown in the accompanying figure, the phosphodiesterase enzyme cleaves DNA between the phosphate and the C-5' atom, thereby producing 3'-nucleotides. In this test, the phosphates on only one of the four nucleotide precursors of DNA (cytidylic acid, for example) are made radioactive with ³²P and DNA is synthesized. Then the DNA is subjected to enzymatic cleavage, in which the radioactive phosphate is transferred to the base that is the 'nearest neighbor' on the 5' side of all cytidylic acid nucleotides. Following four separate experiments, in each of which a different one of the four nucleotide types is radioactive, the frequency of all 16 possible nearest neighbors can be calculated. When Kornberg applied the nearest-neighbor frequency test to the DNA template and resultant product from a variety of experiments, he found general agreement between the nearest-neighbor frequencies of the two. Analysis of nearest-neighbor data led Kornberg to conclude that the two strands of the double helix are in opposite polarity to one another. Demonstrate this approach by determining the outcome of such an analysis if the strands of DNA shown here are (a) antiparallel versus (b) parallel:
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