Cells employ many strategies to avoid genetic mutation. From the high

Question

Cells employ many strategies to avoid genetic mutation. From the high fidelity of DNAsynthesizing enzymes to the pro-death signaling that accompanies mutagenic stimuli such as UV radiation, cellular mechanisms that stymie genetic changes are ubiquitous throughout the natural world. These mechanisms are critical because widespread genomic changes would wreak physiological havoc; indeed, malfunctions in molecular players that safeguard against mutagenesis, such as the protein p53, have been implicated in diseases such as cancer.

Yet despite the criticality of preventing and eliminating DNA mutations to avoid deleterious changes in cells, in specific contexts many organisms have also adapted beneficial mechanisms to induce genetic changes.

One such instance is observed in vertebrate immune systems: white blood cells such as T cells recognize invading pathogens through receptors on their surfaces. In order to recognize a wide variety of pathogens, these cells must generate a large repertoire of receptors. Relying only on a genetically encoded repertoire would be disadvantageously limiting—analogous to having only  a few dozen language phrases with which to respond to the nearly infinite potential combinations of words in a conversation.  Instead, the repertoire is generated by a process of genetic recombination, in which T cells “cut-and-paste” the DNA encoding their microberecognizing receptors. Many of these genetic rearrangements produce cells bearing non-functional proteins; such unproductive cells are eliminated through senescence. Nevertheless, this  seemingly haphazard  process of programmed genetic mutation is crucial to generating immunological diversity, as individuals with defects in this pathway exhibit clinical immunodeficiency. How this process is regulated by T cells to prevent harmful mutations remains the subject of ongoing research.    1 
 Consider each of the answer choices separately and indicate all that apply.

1. Which of the following is true of genetic changes in cells?

A. They can cause serious problems to body systems.
B. They can provide benefits to the immune system.
C. Some genetic mutation is regulated by T cells.

2  
 2. The phrase “seemingly haphazard” ( Highlighted ) is meant to indicate that

(A) the process of programmed genetic mutation deserves further study
(B) the production by T cells of “unproductive cells” is wasteful
(C) genetic recombination may appear random, but is not
(D) T cells are essential to proper immune system functioning
(E) programmed genetic mutation can be dangerous to an organism

3  
 Consider each of the answer choices separately and indicate all that apply.

3. Which of the following can be inferred from the first paragraph of the passage?

A. Pro-death signaling is a mechanism that hinders genetic changes.
B. Cellular mechanisms that safeguard against mutagenesis are very common.
C. Protein p53 may play a role in preventing cancer from forming.

4  
 4. The analogy regarding “a few dozen language phrases ... conversation” ( Highlighted ) is meant to elucidate

(A) why genetic recombination is important to T cell functioning
(B) the need for numerous means of fighting cancer and other diseases caused by cell mutation
(C) why white blood cells such as T cells rely on a genetically encoded repertoire
(D) how language use is like “cutting and pasting”
(E) the mechanism by which mutagenesis can compromise physiological functioning

5  
 Consider each of the answer choices separately and indicate all that apply.

5. In the analogy in the third paragraph, the “nearly infinite potential combinations of words in a conversation” represent

A. pathogens
B. receptors
C. T cells

Sajjad1994 · Answer

OE

1. Which of the following is true of genetic changes in cells?

The first paragraph states that  “widespread genomic changes would wreak physiological havoc,”  such as cancer. The first statement is supported.

The second paragraph adds that  “many organisms have also adapted beneficial mechanisms to induce genetic change.”  In short, some genetic changes are bad, but others are beneficial.

The third paragraph explains how genetic change is important to immune functioning; the second statement is supported. The last line of the passage states  “this process is regulated by T cells to prevent harmful mutations. ” The third statement is also justified.

Answer: A,B,C

Sajjad1994 · Answer

OE

2. The phrase “seemingly haphazard” ( Highlighted ) is meant to indicate that  
 
The word  “seemingly”  indicates that the changes are not really haphazard.  “Seemingly haphazard”  refers to  “programmed genetic mutation.”  The  “this”  in  “this seemingly haphazard process of programmed genetic mutation”  harks back to  “genetic recombination,”  so choice (C) is a match.

Answer: C

Sajjad1994 · Answer

OE

3. Which of the following can be inferred from the first paragraph of the passage?

Pro-death signaling is given in a list of  “cellular mechanisms that stymie genetic changes.” “Stymie”  means  “hinder.”  The first statement is true.

These cellular mechanisms are called  “ubiquitous,”  which means existing everywhere, so certainly they are  “very common.”  The second statement is also true.

The final sentence of the paragraph says that  “malfunctions in molecular players that safeguard against mutagenesis, such as the protein p53, have been implicated in diseases such as cancer.”  Since the malfunction of p53 may cause cancer, it can be inferred that p53, when properly functioning, may work against cancer. The third statement is also true.

Answer: A,B,C

Sajjad1994 · Answer

OE

4. The analogy regarding “a few dozen language phrases ... conversation” ( Highlighted ) is meant to elucidate  
 
According to the passage, T cells need a large repertoire of receptors in order to be able to recognize a wide variety of pathogens. The passage goes on to say that  “ elying only on a genetically encoded repertoire would be disadvantageously limiting—analogous to having only a few dozen language phrases with which to respond to the nearly infinite potential combinations of words in a conversation. Instead, the repertoire is generated by a process of genetic recombination ... ”  According to this analogy, the language phrases are the repertoire of receptors; just as a speaker must respond to a nearly infinite body of language combinations, T cells must also have a large repertoire so they can respond to a wide variety of pathogens. This repertoire is increased through genetic recombination.  Choice (A)  is correct.

Note that  choice (B)  is out of scope,  choice (C)  is the exact opposite of what is being described,  choice (D)  is a distortion based on another analogy in the passage (also, an analogy on the GRE would not be  “meant to elucidate”  another analogy!), and  choice (E)  refers to the first paragraph, not the analogy in question.

Answer: A

Sajjad1994 · Answer

OE

5. In the analogy in the third paragraph, the “nearly infinite potential combinations of words in a conversation” represent

In the analogy referenced, the  “language phrases”  are receptors that can respond to various pathogens. The  “nearly infinite potential combinations of words”  is what a speaker must respond to—the reason a speaker needs a wide repertoire of language. Similarly, the wide variety of pathogens is the reason T cells need such a wide variety of receptors. This supports the first statement only.

Answer: A

Cells employ many strategies to avoid genetic mutation. From the high

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