Genetics - Analysis and Principles

Biology

Quiz 17 :

Non-Coding Rnas

Quiz 17 :

Non-Coding Rnas

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Based on your understanding of the experiment of Figure 17.3, does BrdU enhance the binding of Giemsa to the chromatids or inhibit the binding of Giemsa Explain.
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The experiment of figure 17.3 is based upon harlequin staining technique. In this experiment the chromosome is treated with BrdU (5-bromodeoxyuridine). This nucleotide analog binds to different degree with the stains as compared to the normal chromosomes. When the BrdU treated chromosome are stained then the BrdU containing strand fluoresce brightly than the normal chromatid because it gets less stained due to the presence of BrdU.
Hence, the BrdU inhibits the binding of Giemsa to the chromatids.

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In the data of Figure 19.9, is the solid red phenotype due to chromosome breakage or due to the excision of a TE and chromosomal rejoining Explain how you have arrived at your conclusion. FIGURE 19.9 Evidence for transposable elements in corn. Starting material: The plant contributing the female gamete was homozygous for a chromosome carrying c sh Wx. The male pollen of the corn plant was homozygous for a chromosome in which the Ds element had moved into the C gene: CDsC Sh wx. img img
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In the observations of figure 17.11, the solid red phenotype was due excision of the transposable element (which is Ds locus in this case). The Ds was when present next to the C allele, it produced colorless kernels by suppressing the property of C allele of producing red phenotype. But when it was excised off to some other site then the kernel again became reD.We came to this conclusion by the following When the crossing of female eggs (containing Ds bound C allele) was done with male eggs (containing free C allele) then one of the resultant daughter chromosomes had changes. The change was that in one of the chromosome, the Ds locus has left its site near C allele and has excised off to some other site. This made C allele again active and it expressed its property of providing red color to the kernel. This observation is shown below in the diagram:
img Hence, from the above explanation we concluded that the solid red phenotype is due to the excision of the transposable element.

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Make a list of the differences between the Holliday model and the double-strand break model.
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Differences between the Holliday model and the double strand break model :
• In Holliday model, during strand invasion and intertwining of the complementary strands of two homologs with similar chromatids occurs. An X-shaped connection is formed between them that is called Holliday junction.
While in case of double strand break model, the homologous chromatids are intertwined by forming a D loop in between them.
• During the formation of Holliday junction, one strand of each homologous chromatid is nicked at similar points, which then undergo Holliday junction formation.
While in case of double strand break model, both the strands of the same chromatid (recessive chromatid) are nicked, which then undergo initiation of D loop formation by the unnicked strand of the dominant chromatiD.• The Holliday junction formed migrate from the point of its formation to the opposite end of the strand leading to the complete reversal of the base pairs of one strand each of the two homolog chromatids. But the D loop forms at a certain point and do not migrate from its generation point.

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In the Holliday model for homologous recombination (see Figure 19.2), the resolution steps can produce recombinant or nonrecombinant chromosomes. Explain how this can occur. FIGURE 19.2 The Holliday model for homologous recombination. The Holliday model is adapted from Holliday R. (1964) A mechanism for gene conversion in fungi. Genet Res 5, 282-304. img img img
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Is homologous recombination an example of mutation Explain.
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What two molecular mechanisms can explain the phenomenon of gene conversion Would both occur in the double-strand break model
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With the harlequin staining technique, one sister chromatid appears to fluoresce more brightly than the other. Why
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What is gene conversion
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Make a list of the similarities and differences among homologous recombination, site-specific recombination, and transposition.
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Let's suppose that a researcher followed the protocol described in the experiment of Figure 17.3 but exposed the cells to BrdU for three cell generations instead of two. Near the end of growth, the cells were exposed to colcemid to prevent them from completing mitosis following the third round of DNA replication. What would be the expected results if a parental cell contained a total of four chromosomes (two homologous pairs) and a single sister chromatid exchange occurred after the second replication Your drawing should show four cells that contain four condensed chromosomes in each cell.
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Which steps in the double-strand break model for recombination would be inhibited if the following proteins were missing Explain the function of each protein required for the step that is inhibited. A. RecBCD B. RecA C. RecG D. RuvABC
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Describe the similarities and differences between homologous recombination involving sister chromatid exchange (SCE) and that involving homologus. Would you expect the same types of proteins to be involved in both processes Explain.
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Briefly explain how McClintock determined that Ds was occasionally moving from one chromosomal location to another. Discuss the type of data she examined to arrive at this conclusion.
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Based on your current knowledge of genetics, discuss whether or not you think the selfish DNA hypothesis is correct.
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In the data shown here, harlequin staining was used to determine the frequency of sister chromatid exchanges (SCEs) in the presence of a suspected mutagen. img
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In your own words, explain the term transposon tagging.
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In the experiment described in experimental question E2, at what point would you need to add the mutagen: before the first round of DNA replication, after the first round but before the second round, or after the second round
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If homologous recombination could not occur, what would be the harmful and beneficial consequences
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What are recombinant chromosomes How do they differ from the original parental chromosomes from which they are derived
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The molecular mechanism of SCE is similar to homologous recombination between homologs except that the two segments of DNA are sister chromatids instead of homologous chromatids. If branch migration occurs during SCE, will a heteroduplex be formed Explain why or why not. Can gene conversion occur during sister chromatid exchange
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