LR Question 12 Explanation, by LSATHacks
QUESTION TEXT: Populations of a shrimp species at eleven different…
QUESTION TYPE: Paradox
PARADOX: Different reefs contain shrimp with big genetic differences. Yet, ocean currents should allow the shrimp to interbreed.
ANALYSIS: For paradox questions, you must think carefully about what you’re trying to explain. The question doesn’t always spell it out for you. Figure out the paradox before you look at the answers.
Here, the shrimp can travel between reefs. So they could interbreed. But there are large genetic differences between reefs. This suggests the shrimp don’t interbreed.
Answer B is very tricky. There will always be some genetic differences within a population. But, the differences might be very small, and not matter.
The paradox in the stimulus is that there are large genetic differences between reefs.
___________
- This just tells us that shrimp are similar to each other. That makes sense. It’s like how you have more genetic heritage in common with a Norwegian than with an Elephant.
This information doesn’t explain why you do have some genetic differences from Norwegians despite easy air travel. - This is very tempting. But the stimulus said there are substantial genetic differences from one reef to another. Whereas this answer choice just says there are ‘differences’. It could be that within a reef there are only tiny differences. We need to explain large differences between reefs.
- CORRECT. This shows that even though shrimp could breed at other reefs, they don’t. Shrimp come home to breed.
- This answer adds to the confusion. If shrimp leave reefs when they’re old enough to breed, then presumably they breed with shrimp at other reefs. Why are there still big genetic differences?
- This doesn’t affect anything. We don’t care about shrimp that left coral reefs to live in the open ocean. The stimulus refers to genetic differences among the shrimp that stayed at reefs.
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The stimulus says, “Populations of a shrimp species at eleven different Indonesian coral reefs show substantial genetic differences from one another. This is surprising because the area’s strong ocean currents probably carry baby shrimp between the different reefs, which would allow the population to interbreed and become genetically indistinguishable.”
I picked answer choice “E” – “Ocean currents probably carry many of the baby shrimp hatched at a given Indonesian coral reef out into the open ocean rather than to another coral reef” The prompt tells us that we may take the statements as “true”. The original stimulus says that the currents PROBABLY carry baby shrimp between different reefs, but it can also be true that instead, they are taken out to sea. If they are taken out to sea, they won’t have a chance to interbreed. They won’t even have a chance to see each other. This also explains why the population of said shrimp species are so genetically different from one another. The “rather than to another coral reef” would mean that our perceived mode of transportation between the different reefs are cut off.
Answer choice “C” states – “Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched.” If this were true, it means that they are only back at their own coral reef for breeding. This would also mean, that if not for breeding, they would be at whichever coral reef they drifted to. If they are at whichever coral reef they drifted to, then they are caught and examined along with the local shrimp found at that location. Then instead of each coral reef having their own distinct genetic species of shrimp, the researchers would find many different shrimp from the various reefs intermingled together. They may not breed with one another, but the fact they the various genetically different shrimps are all together across the multiple reefs would make it difficult to conclude that they are distinct from one another, and from differing reefs.
I think it is more so related to the support of the conclusion that the strong ocean currents would allow the shrimp to interbreed, and become genetically indistinguishable.
Because the shrimp return to the originally breeding population, this interbreeding does not happen, which in turn, does not allow the populations to become “indistinguishable.” Thus, providing a strong explanation.
As for your explanation of choice E:
There is a chance that no baby shrimp will reach a different reef, but there is a chance that all the baby shrimp will reach a different reef. Many =/= all. As long as there is a possibility that the baby shrimp can reach another reef, there is a possibility that interbreeding can happen, thus different populations become indistinguishable (which is basically what the support for the conclusion suggests.)