LSAT 147 – Section 4 – Question 22

LSAT 147 - Section 4 - Question 22

September 2016

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Question QuickView	Type	Tags	Answer Choices	Curve	Question Difficulty	Psg/Game/S Difficulty	Explanation
PT147 S4 Q22	+LR	Strengthen +Streng Link Assumption +LinkA	A 25% 160 B 13% 159 C 49% 167 D 4% 157 E 10% 160	158 164 170	+Hardest	146.282 +SubsectionMedium

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.

Summarize Argument

The author concludes that the hepadnavirus present in the chromosomes of a zebra finch and dark-eyeed junco is at least 25 million years old. This is because after a hepadnavirus inserts itself into a chromosome of an animal, it’s based on to all of that animal’s descendants. In addition, the hepadnavirus is found in the same location in the corresponding chromosome of the finch and the junco. And, these two species diverged around 25 million years ago.

Notable Assumptions

The author assumes that having a hepadnavirus in the same corresponding location in the chromosome tells us something about when the hepadnavirus was inserted. The author also assumes the hepadnavirus didn’t insert itself into each bird’s chromosome more recently than 25 million years ago.

Viruses can affect the evolution of an organism and can thereby influence the likelihood of their diverging into two species.

This suggests viruses might have influenced the divergence of the two species. But this doesn’t suggest anything about the age of the hepadnavirus. Perhaps other viruses caused the species to diverge, and the hepadnavirus was inserted in each chromosome after divergence.

The chromosomes of the zebra finch and the dark-eyed junco contain fragments of no virus other than the hepadnavirus.

This tells us there’s no other virus in the chromosomes of the birds. But this doesn’t reveal anything about the age of the hepadnavirus.

When a virus inserts itself into an animal’s chromosome, the insertion occurs at a random spot.

This strengthens by casting doubt on the possibility that the virus inserted itself into each chromosome after the divergence 25 million years ago.

Many bird species other than the zebra finch and the dark-eyed junco contain fragments of the hepadnavirus.

The presence of the virus in other birds has no clear impact on how long the virus has been around.

The presence of a hepadnavirus in an animal species does not affect the likelihood of that species’ survival.

Whether the virus affects chances of a species’ survival has no clear impact on how long the virus has been around.

LSAT 147 – Section 4 – Question 22

LSAT 147 - Section 4 - Question 22

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Review Results

LSAT PrepTest 147 Explanations

Section 1 - Logical Reasoning

Section 2 - Reading Comprehension

Section 3 - Reading Comprehension

Section 4 - Logical Reasoning

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