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 microbe recognizing 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.

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

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.



The phrase "seemingly haphazard" 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



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

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.



The analogy regarding "a few dozen language phrases ... conversation" 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



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

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