PrepTest 114, Section 4, Question 15
Loggerhead turtles live and breed in distinct groups,(55 more words not shown)
Which one of the following,(8 more words not shown)
- ANesting sites of(20 more words not shown)
- BThe distance between(14 more words not shown)
- CLoggerhead hatchlings in(24 more words not shown)
- DNinety-five percent of(15 more words not shown)
- ECommercial aquariums have(13 more words not shown)
Reading the argument
How distinctive is that DNA match?
The proposed journey is striking: turtles feeding near Baja may have hatched 10,000 kilometers away in Japanese waters. The DNA evidence sounds relevant. But it only identifies Japan as the source if the match helps distinguish those turtles from turtles originating elsewhere.
What if separate populations share the features being compared? The Baja and Japanese samples could match even if the Baja turtles hatched at another site. We need to know whether this kind of match is unusual outside the Japanese group, not simply be impressed by the number 95 percent.
What we’re looking for
For a weakener, I'd look for evidence that the same match occurs more broadly. Be precise about that percentage: 95 percent of the samples match. The passage isn't saying each turtle shares 95 percent of its entire genetic code with another turtle.
Working the answers
- A
These other nesting sites offer possible places to investigate, but their existence doesn't connect the particular Baja juveniles to them. The original conclusion could remain true even with other Pacific nesting sites. A gives us an alternative location without evidence that explains away the match with Japan.
- B
Atlantic turtles traveling a shorter distance doesn't establish a limit on how far Pacific turtles travel. Different groups could have different distances between hatching and feeding sites. B doesn't challenge the DNA evidence or show that the proposed Pacific journey is implausible.
- C
A decline in Japan paired with stability near Baja sounds worth examining. But what is being counted? Japan's figure concerns hatchlings. Baja's figure concerns nesting sites, not the number of juvenile turtles feeding there.
The same number of nesting sites could contain different numbers of turtles over time. Nor are those local nesting sites the source of the feeding juveniles according to the proposed explanation. C therefore doesn't establish the population mismatch it may initially seem to show. It compares different measures instead of showing that the Baja juveniles' numbers stayed constant while their supposed source population fell.
- DCorrect
The Baja samples match Atlantic samples at the same reported rate. The match therefore doesn't single out the Japanese nesting population as effectively as the argument suggests. A result shared with a quite different group is less useful for identifying this particular origin.
This is the broader matching pattern we predicted. It doesn't prove the Baja turtles came from the Atlantic or that they couldn't have come from Japan. It shows why the DNA result, by itself, may not distinguish where they hatched. That directly weakens the connection between the evidence and the proposed journey.
- E
Successful breeding in aquariums doesn't tell us where these wild juveniles hatched. The ability to breed Atlantic and Pacific turtles together is a different question from whether the Baja group's DNA identifies a Japanese origin. E doesn't establish that the aquarium breeding produced these turtles or accounts for the matching samples.
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