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TLS Online TPP Program

#Question id: 2884

When the temperature of a solution of DNA is raised to near the boiling point of water, the optical density, (called absorbance) at 260 nm markedly increases, a phenomenon known as hyperchromicity. Which of the following statement is INCORRECT from the given set of statements?

#Unit 2. Cellular Organization

  1. The explanation for this increase is that duplex DNA absorbs more ultraviolet light by ~40% than do individual DNA chains.

  2. This hyperchromicity is due to base stacking, which increases the capacity of the bases in duplex DNA to absorb ultraviolet light.

  3. The sharpness of the increase in absorbance at the melting temperature tells us that the denaturation and renaturation of complementary DNA strands is a highly cooperative, zippering-like process.

  4. At high ionic strength, the negative charges are shielded by cations, thereby destabilizing the helix. Conversely, at low ionic strength, the unshielded negative charges render the helix more stable.

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TLS Online TPP Program

#Question id: 5295

#Unit 8. Inheritance Biology

A cross is made between an Hfr that is met+ thi+ pur+ and an F-that is met- thi- pur-. Interrupted mating studies show that met+ enters the recipient last, so met+ recombinants are selected on a medium containing supplements that satisfy only the pur and thi requirements.  These recombinants are tested for the presence of the thi+ and pur+ alleles. The following numbers of individuals are found for each genotype:

A) Gene Order

I

Thi Pur  Met

II

Pur  Met  Thi

III

Pur   Thi  Met

B) Distance between Pur and Thi

IV

15.4 map unit

V

1.8 map unit

What is the following correct combination?
TLS Online TPP Program

#Question id: 5296

#Unit 8. Inheritance Biology

A transformation experiment is performed with a donor strain that is resistant to four drugs: A, B, C, and D. The recipient is sensitive to all four drugs. The treated recipient cell population is divided up and plated on media containing various combinations of the drugs. The table below shows the results. What is the probable order of the three tightly linked genes?  
TLS Online TPP Program

#Question id: 5297

#Unit 8. Inheritance Biology

In a generalized transduction experiment, phages are collected from an E. coli donor strain of genotype cys+ leu+thr+ and used to transduce a recipient of genotype cys_ leu_ thr_. Initially, the treated recipient population is plated on a minimal medium supplemented with leucine and threonine. Many colonies are obtained. These colonies are then replica-plated onto three different media: What is order of gene?
TLS Online TPP Program

#Question id: 5298

#Unit 8. Inheritance Biology

Four E. coli strains of genotype a+ b− are labeled 1, 2, 3, and 4. Four strains of genotype a− b+ are labeled 5, 6, 7, and 8. The two genotypes are mixed in all possible combinations and (after incubation) are plated to determine the frequency of a+ b+ recombinants. The following results are obtained, where M = many recombinants, L = low numbers of recombinants, and 0 = no recombinants. On the basis of these results, assign a sex type (either Hfr, F+, or F−) to each strain
TLS Online TPP Program

#Question id: 5299

#Unit 8. Inheritance Biology

One particular group of mutant strains specifically required the amino acid arginine to grow, and these arginine auxotrophs formed the basis of their subsequent analysis, given in table 
TLS Online TPP Program

#Question id: 5300

#Unit 11. Evolution and Behavior

What is metagenomics?