Populations of a shrimp species at eleven different Indonesian coral

Question

Populations of a shrimp species at eleven different Indonesian coral reefs show substantial genetic differences from one reef to another. This is surprising because the area’s strong ocean currents probably carry baby shrimp between the different reefs, which would allow the populations to interbreed and become genetically indistinguishable.

Which one of the following, if true, most helps to explain the substantial genetic differences among the shrimp populations?

(A) The genetic differences between the shrimp populations are much less significant than those between shrimp and any other marine species.

(B) The individual shrimp within a given population at any given Indonesian coral reef differ from one another genetically, even though there is widespread interbreeding within any such population.

(C) Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched.

(D) Most shrimp hatched at a given Indonesian coral reef are no longer present at that coral reef upon becoming old enough to breed.

(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.

Source: LSAT

pushpitkc · Answer

The argument states that despite being carried away from their original reef,
the shrimp(species) are genetically different at each reef, where as 
they should be similar since few of the shrimp at each reef are available at each reef.

But,  Option C (Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched)
 resolves the discrepancy because, if before breeding each of the species return to their original place, there will be genetic diversity at each reef.

stne · Answer

But if interbreeding itself does not lead to genetic similarities , then even if they did not return back to their original reef , and did indeed interbreed then also there would be genetic differences . This could also explain the discrepancy.

This is what option B says, it says even within a particular reef there is wide genetic differences even though there is interbreeding , so these same shrimps when transferred to other reefs and after interbreeding could lead to the same result, i.e. genetic differences would be prevalent.

So why is B wrong?

Lucy Phuong · Answer

Hi,

I think you're questioning the premise - " which would allow the populations to  interbreed and become genetically indistinguishable  ", which should be taken as a fact.

Actually, information provided by option (B) is not related to the paradox needed to be solved. We need to find out why  interbreeding between DIFFERENT populations from DIFFERENT coral reefs  results in genetics differences, while option (B) focuses on  interbreeding between individuals of the SAME population in the SAME reef . U see? This information doesn't help. (B) is gone.

HeadingEast · Answer

Nowhere does it state that interbreeding actually occurs. It simply states that interbreeding would be potentially occur given that genetically different shrimp do come into contact with each other. One way to resolve this paradox would be to prove that interbreeding does not occur even if it is "possible". Answer choice C does just that - It explains why shrimp may not interbreed even though they do come in contact with one another.

Lucy Phuong · Answer

Oh yes, my mistake. The above is not a proper explanation, I admit. Thank you.

kudos to you!

gmatexam439 · Answer

Answer:C

Populations of a shrimp species at eleven different Indonesian coral reefs show substantial genetic differences from one reef to another. This is surprising because the area’s strong ocean currents probably carry baby shrimp between the different reefs, which would allow the populations to interbreed and become genetically indistinguishable.

Which one of the following, if true, most helps to explain the substantial genetic differences among the shrimp populations?

(A) The genetic differences between the shrimp populations are much less significant than those between shrimp and any other marine species. - We are not worried about the other marine species. 
(B) The individual shrimp within a given population at any given Indonesian coral reef differ from one another genetically, even though there is widespread interbreeding within any such population. - We need not be worried about the distinction among the shrimp at a given location. We are worried about the shrimps' DNA at 11 different locations. 
(C) Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched. - CORRECT. It tells us that even though the shrimps are carried to other coral reefs by ocean currents, they are go back to their native place before breeding, which is responsible for the reduction in diversity. 
(D) Most shrimp hatched at a given Indonesian coral reef are no longer present at that coral reef upon becoming old enough to breed. - Irrelevant 
(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. - It is a possibility that is not refuted by the author. But it definitely doesn't help us explain the genetic diversity, because some shrimps are definitely carried over to other coral reefs.

Hope it helps !!
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Give kudos if this helped !

akela · Answer

Powerscore explanation:

sunny91 · Answer

gmatexam439 .

madhukaramar · Answer

Populations of a shrimp species at eleven different Indonesian coral reefs show substantial genetic differences from one reef to another. This is surprising because the area’s strong ocean currents probably carry baby shrimp between the different reefs, which would allow the populations to interbreed and become genetically indistinguishable.

Which one of the following, if true, most helps to explain the substantial genetic differences among the shrimp populations?

Interesting Question !!! .Here is my thought process - 
What are we looking for - There are differences among the species of shrimps in different coral reef, but the source of all the shrimps are same. What could be the reason of the difference ??

(A) The genetic differences between the shrimp populations are much less significant than those between shrimp and any other marine species.
 -- Irrelevant. We are not concerned about other marine species.

(B) The individual shrimp within a given population at any given Indonesian coral reef differ from one another genetically, even though there is widespread interbreeding within any such population.
-- We are not concerned about the difference among the shrimps of the same coral reef. We need a reason for the difference among species found in different coral reef.

(C) Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched.
-- So if they travel back to their own reef before breeding ,they may get features specific to the local reef. Keep it.

(D) Most shrimp hatched at a given Indonesian coral reef are no longer present at that coral reef upon becoming old enough to breed.
-- We are not concerned with this fact.

(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.
-- This choice does n't help. It conveys that there should be more similarities among the shrimp species of different reef. Not , what we are looking.

C is the best choice.

Krishnahelps · Answer

Hi, can someone pls explain the stimulus. If it's saying that baby shrimps from different reefs get carried away by the current and there is a possibility that they will interbreed(breeding between different race) and become genetically indistinguishable. I didn't understand how interbreeding will make them genetically indistinguishable? Shouldn't it create an altogether different species? Please help here.

Krishnahelps · Answer

Hi, can someone pls explain the stimulus. If it's saying that baby shrimps from different reefs get carried away by the current and there is a possibility that they will interbreed(breeding between different race) and become genetically indistinguishable. I didn't understand how interbreeding will make them genetically indistinguishable? Shouldn't it create an altogether different species? Please help here.

8Harshitsharma · Answer

Krishnahelps

I'll try to explain it. Even though for this particular problem getting a gist of it is more important than exactly knowing how it'll happen.

The author is saying that baby shrimps from reef1 may get carried by ocean currents to the other reefs (2,3...11), and there these shrimps reproduce with the indigenous shrimp species and produce some offspring (say offspring1_5)- which would have dominant genes from each parent (reef1 shrimp parent and few from the new reef shrimp parent say reef5). Similarly, as per the author, a baby shrimp from reef5 gets carried to reef1, creating a genetically identical shrimp to offspring1_5. The assumption is that there is an equal chance for each reef's shrimp species to mate with each of the other reef's species. You repeat this process over and over for thousands of years, and as there is only a limited number of genes that an organism can have, you'll have only one genetic combination (with all the  dominant  genes), possibly a complex hybrid but importantly THE SINGLE MOST DOMINANT ONE.

It is all just Darwin's stuff prolly.

Vineet921 · Answer

Could you please help in explaining why B is not the right answer.

Vineet921 · Answer

Can you explain how B is not right.  GMATNinja

WhitEngagePrep · Answer

Let's attack this one from the start: 1. Identify the Question Type "most helps to explain" along with a quick look up at the argument and seeing the word "surprising" = Resolve a Paradox or Surprise 2. Deconstruct the Argument Since it's a paradox, our job is to get clear on what is surprising? Map the argument's cause and possible effect chain first: currents are strong (fact) -(1)-> baby shrimp carried -(2)-> populations interbreed -(3)-> populations become genetically indistinguishable Note that everything after the strong currents is a conjecture and therefore isn't necessarily going to come true. So what is the surprise?? That this chain breaks down somewhere because these 11 reefs have substantial genetic differences from one reef to another... Our job - figure out WHY (or where the breakdown happened). 3. Pause and Plan So this could break down at any arrow... the currents are strong but (1) maybe the baby shrimp aren't being carried. Or maybe they are being carried but (2) the interbreeding we expected isn't happening. Or maybe the interbreeding is happening, but (3) it isn't causing the genetic variation we'd expect. Or it could even be that we do get genetic variation but then something else (an externality) comes along and wipes out that variation! I have no clue what its going to be, but any of those arrows breaking down would "explain the surprising finding." 4. Eliminate I'll start with A, D, and E and come back to your question about B and correct answer C. A - don't care about "other marine species," out of scope - Eliminate D - if anything this would support the arrows because shrimp are hatching and then somewhere else breeding (first and second arrows hold) - Eliminate E - because this only applies to some of the shrimp, this technically doesn't really knock out an arrow, the shrimp NOT carried into the open ocean could still be upholding the expected chain of events - Eliminate Now your question about B . You didn't provide any justification for why you liked B, but I do think one possible tempting bit of logic might be the following... "It shows that even with interbreeding, you can still get genetic variation. So maybe it’s not surprising that the populations look different." SO TEMPTING, but don't forget that this is a PARADOX question - we're not here to strengthen the fact that genetic variation is occurring (that's a fact, we know that's what we have at those 11 different sites). We're trying to figure out HOW this variation is still occurring, and B offers no mechanism. Also, you might make the argument that B could be "out of scope" since we don't know that we can make cross-location inferences from a within-location occurrence. So either this simply echos (and therefore heightens) the weird outcome we're seeing, or can't be used because it's not the right comparison. But either way, we eliminate this choice! Okay, the correct answer C. If this is true, then arrow (2) is failing. The shrimp aren't interbreeding! Hope this helps!

Whit

Populations of a shrimp species at eleven different Indonesian coral

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Populations of a shrimp species at eleven different Indonesian coral

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