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After a hepadnavirus inserts itself into a chromosome
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04 Sep 2017, 02:50
04 Sep 2017, 02:50
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A
B
C
D
E
Difficulty:
95%
(hard)
Question Stats:
31% (02:15) correct
69%
(02:21)
wrong
based on 846
sessions
After a hepadnavirus inserts itself into a chromosome of an animal, fragments of the virus are passed on to all of that animal's descendants. A hepadnavirus fragment is present in a chromosome of the zebra finch and in precisely the same location in a corresponding chromosome of the dark-eyed junco. The fact that these two bird species diverged from each other about 25 million years ago therefore means that the hepadnavirus is at least 25 million years old.
Which one of the following, if true, most strengthens the argument?
(A) Viruses can affect the evolution of an organism and can thereby influence the likelihood of their diverging into two species.
(B) The chromosomes of the zebra finch and the dark-eyed junco contain fragments of no virus other than the hepadnavirus.
(C) When a virus inserts itself into an animal's chromosome, the insertion occurs at a random spot.
(D) Many bird species other than the zebra finch and the dark-eyed junco contain fragments of the hepadnavirus.
(E) The presence of a hepadnavirus in an animal species does not affect the likelihood of that species' survival.
Source: LSAT
Which one of the following, if true, most strengthens the argument?
(A) Viruses can affect the evolution of an organism and can thereby influence the likelihood of their diverging into two species.
(B) The chromosomes of the zebra finch and the dark-eyed junco contain fragments of no virus other than the hepadnavirus.
(C) When a virus inserts itself into an animal's chromosome, the insertion occurs at a random spot.
(D) Many bird species other than the zebra finch and the dark-eyed junco contain fragments of the hepadnavirus.
(E) The presence of a hepadnavirus in an animal species does not affect the likelihood of that species' survival.
Source: LSAT
Re: After a hepadnavirus inserts itself into a chromosome
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10 Sep 2017, 08:52
10 Sep 2017, 08:52
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Expert Reply
arvind910619 wrote:
I am totally confused by the answer to this question
I thought the answer is A
Experts please explain the answer as the argument does not talks about the pattern of insertion of the chromosome.
I thought the answer is A
Experts please explain the answer as the argument does not talks about the pattern of insertion of the chromosome.
We are told that "a hepadnavirus fragment is present in a chromosome of the zebra finch and in precisely the same location in a corresponding chromosome of the dark-eyed junco."
But what if the virus always inserts itself in the same location whenever it infects an animal? If that were the case, the fact that the virus is present in the same location in two animals would not be strong evidence that the virus must have entered that location before the two animals diverged. In that case, the virus could have entered the two animals independently at any point in time.
Quote:
(C) When a virus inserts itself into an animal's chromosome, the insertion occurs at a random spot.
Choice (C) tells us that the location is random, which means it would be highly unlikely that the virus entered the two animals independently. This suggests that the virus likely entered that location before the two animals diverged 25 million years. This, in turn, supports the conclusion that the virus is at least 25 million years old.
Quote:
(A) Viruses can affect the evolution of an organism and can thereby influence the likelihood of their diverging into two species.
Choice (A), on the other hand, does not give us any reason to believe that the virus likely entered that location before the two animals diverged. This statement is much too general to suggest that the specific hepadnavirus discussed in the passage is what caused the animals to diverge. There could have been numerous other viruses affecting the organism more than 25 million years ago, and we have no idea whether this specific hepadnavirus was one of them.
Choice (C) is the best answer.
General Discussion
Re: After a hepadnavirus inserts itself into a chromosome
[#permalink]
04 Sep 2017, 07:50
04 Sep 2017, 07:50
1
Kudos
ganand wrote:
After a hepadnavirus inserts itself into a chromosome of an animal, fragments of the virus are passed on to all of that animal's descendants. A hepadnavirus fragment is present in a chromosome of the zebra finch and in precisely the same location in a corresponding chromosome of the dark-eyed junco. The fact that these two bird species diverged from each other about 25 million years ago therefore means that the hepadnavirus is at least 25 million years old.
Which one of the following, if true, most strengthens the argument?
(A) Viruses can affect the evolution of an organism and can thereby influence the likelihood of their diverging into two species.
(B) The chromosomes of the zebra finch and the dark-eyed junco contain fragments of no virus other than the hepadnavirus.
(C) When a virus inserts itself into an animal's chromosome, the insertion occurs at a random spot.
(D) Many bird species other than the zebra finch and the dark-eyed junco contain fragments of the hepadnavirus.
(E) The presence of a hepadnavirus in an animal species does not affect the likelihood of that species' survival.
Source: LSAT
Which one of the following, if true, most strengthens the argument?
(A) Viruses can affect the evolution of an organism and can thereby influence the likelihood of their diverging into two species.
(B) The chromosomes of the zebra finch and the dark-eyed junco contain fragments of no virus other than the hepadnavirus.
(C) When a virus inserts itself into an animal's chromosome, the insertion occurs at a random spot.
(D) Many bird species other than the zebra finch and the dark-eyed junco contain fragments of the hepadnavirus.
(E) The presence of a hepadnavirus in an animal species does not affect the likelihood of that species' survival.
Source: LSAT
The chromosomes of the zebra finch and the dark-eyed junco contain fragments of the hepadnavirus at the same location. What if that virus inserts itself into the same location of an animal's chromosome? Then we can't conclude that that virus is at least 25 million years old because it is possible that the hepadnavirus has inserted itself into these two kinds of birds. Hence C strengthens the argument.
