Q10 - In an experiment, scientists changed

[walkerdoreen07]

Hello,
Can't seem to figure out the logic argument Q10? I chose "D" which is wrong answer. I chose "D" because it says in passage that "otherwise identical genes had normal vision"

D mentions no effect on flies other than lack of ultravioent. I think my thinking is off.

Can you explain?

Thank you!
Doreen

[ManhattanPrepLSAT1]

Necessary Assumption

We know that when a fly lacks has damage to a particular gene then the fly will lack ultraviolet vision. Identical flies without this damaged gene have normal vision.

Does that mean that if a fly has damaged vision, that fly will necessarily have the damaged gene? Maybe the combined effects of three separate genes control a fly’s vision. Damage to any one of them would lead to impaired vision. If that were the case then if you encountered a fly with damaged vision, you wouldn't know for certain which of the genes had been damaged.

The only way the conclusion reached in the argument could follow is if only one gene controlled the fly's ultraviolet vision. Then, anyone who observed a fly with impaired vision would know that the impairment was caused by damage to the one gene.

Correct Answer
Answer choice (B) is a necessary assumption of the argument. Try negating it. If other genes were required in the formation of ultraviolet vision, then impaired vision could be a result of damage to other genes (not just the one that was discussed in the conclusion of the argument).

Incorrect Answers
(A) is helpful, but not necessary. It doesn't need to be well understood. So long as the relationship between genes and a fly’s ultraviolet vision is understood, the argument’s fine.
(C) is not necessary. This argument is not about all species of flies, just the species being discussed.
(D) is irrelevant. Other sorts of effects are not being discussed in this argument.
(E) undermines the argument. This argument concludes that ultraviolet vision is genetically determined - not environmentally determined.

[walkerdoreen07]

Thank you. i have to redo.

[sgorginian]

Matt,

I quickly narrowed it down to B and D. After your explanation, i see why it has to be B. Negating is a great method.

However, I would like to elaborate on D, because that is what i chose same as the original poster. I think he or she chose D for the same thought reasoning i had.

I told myself, "the author assumes that the gene change had no effect on the flies other than the lack of ultraviolet vision cells".

My thought was, yes this makes sense because if the gene change HAD an effect on the flies other than vision cells, for instance the gene changed changed something else that in turn had an effect on the ultra violet vision then this would explain the results. So the author is assuming that this gene change they did had no other effect on something else that might have led to th e results.

[ManhattanPrepLSAT1]

I totally see your position. It's an attempt to find another cause. And I think you're saying that answer choice (D) rules out an alternative cause, by saying that there was no other effect.

But if something else is responsible for ultraviolet vision that would run counter to the stimulus. The argument says that the cells that give flies their ultraviolet vision are these vision cells mentioned.

So I think we have to stick with the text... Good work though!

[mcop730]

I had a similar problem with this question. I quickly narrowed it down to B and D, but chose D. I think I see why B is correct, as the focus is on the ultra violet vision cells, rather, than any other effects the gene may have had, which seems irrelevant now, and out of scope. However, I am having trouble identifying the exact core of the argument.

Could you please help me with this?
Thanks!
Mara

[foralexpark]

I had a similar problem with this question. I quickly narrowed it down to B and D, but chose D. I think I see why B is correct, as the focus is on the ultra violet vision cells, rather, than any other effects the gene may have had, which seems irrelevant now, and out of scope. However, I am having trouble identifying the exact core of the argument.

Could you please help me with this?
Thanks!
Mara

Let me try to clarify this.. (i hope it isn't too late)

so core is..

premise: change single gene X -> lack ultra vision
conclusion: lack ultra vision -> damage in that gene X

so the answer (a) says that gene X is the ONLY thing that affects ultra vision. This MUST be assumed in order for the conclusion to hold, because if it doesn't, and say that there are other genes that could equally affect ultra vision, then the conclusion is obviously flawed (it becomes susceptible to reversal logic error)

[WaltGrace1983]

I am REALLY confused by this stimulus. Even so, I understand why A, B, and E are wrong. Can someone please help me to understand what the stimulus is actually saying here? I am warning you now that this post may be incomprehensible.

I think the wording of this question is really confusing, possibly because of vagueness. We know that there are two sets of flies. We know that these two sets of flies are both cloned. We know that these flies have the same exact genes in the same exact numbers. It would have made more sense to me to phrase the question like this: "In an experiment, scientists changed a single gene in cloned flies of a certain species. SOME cloned flies lacked the eye cells...even though OTHERS with identical genes had normal vision." I think I got confused when it said "unaltered," perhaps because I was thinking that these were the "original" flies - the flies without this new set of genes. I don't know though. Here is how the argument goes:

- There are these cloned flies that had one gene changed by scientists. Let's say their genes are a,b,c,d, and f. F is the changed gene (it used to be E until scientists changed it)
- However, these flies now lack the cells that give them UV vision while (and here is where I get confused) some flies had normal vision with the same exact cells. Therefore, there are two flies. Both have a, b, c, d, and f genes but one has UV vision and the other does not.
- Therefore, species lacking this UV vision must have DAMAGED genes, rather than an absence of genes or something.

I picked (B) out of elimination. I eliminated (D) because whether or not it had any other effect rather than vision is unimportant here. Let's say it affected memory....ok great but that doesn't matter!

I guess where I am getting confused is this: let's say (B) is correct - and apparently it must be correct if it is a necessary assumption for the argument. If (B) is correct then we can clearly see why the argument stands the way it is. If both of these flies have the same genes but one has UV vision and the other doesn't then we must know there is a problem with one of the genes. Ok, awesome!

However, I guess where I am getting confused is when I take the negation. The negation would say "At least one other gene in the flies in the experiment is required for the formation of the UV vision cells." If we assume the negation as the case and we put it in with the argument it would go like this:

P: "Cloned flies with identical genes had different situations: one has UV vision and the other does not"

"At least one other gene in the flies in the experiment is required for the formation of the UV vision cells"

C: "Flies of this species lacking UV vision must have some damage to this gene."

I guess where I am getting confused is that, when I negate this to "check" my answer, I think to myself "but we already know that the genes are absolutely identical with no differences." It would be different if the stimulus said that "every fly with UV vision possesses all the genes that the fly without UV vision has." This would leave the opportunity for the flies to have different numbers of genes, and thus would also leave the opportunity for the fly with UV vision to have genes a, b, c, d, f, AND g or something like that. Because of this contradiction when I negate the assumption, is this exposing the nature of why the assumption is actually correct?

When I was doing this timed my head was spinning but I knew that (B) was getting at SOMETHING. That "something" just happened to be correct.

However, wouldn't (D) also be wrong because anything that happened to one set of flies (the ones with UV vision) also happened to the other set of flies (the ones without UV vision)? That is, even if lets say the gene change caused the flies to have a problem with the oxygen flow throughout their body and THIS is what caused some weirdness in the eye cells, this would be true for BOTH. Therefore, even if we accept that there was some kind of effect other than on the UV vision cells directly, this doesn't really matter does it? I hope this all makes sense!

[maryadkins]

- However, these flies now lack the cells that give them UV vision while (and here is where I get confused) some flies had normal vision with the same exact cells. Therefore, there are two flies. Both have a, b, c, d, and f genes but one has UV vision and the other does not.

This is where you take a wrong turn. The flies that have normal vision do NOT have a b c d f in your example. They have a b c d e.

"These cloned flies lack...UV vision, even though cloned siblings with unaltered, otherwise identical genes..."

The "otherwise" identical means the two groups of flies have everything the same BUT the UV gene.

Hopefully this clarifies your specific concerns about answer choices (B) and (D), but let me know if it doesn't.

[lsatzen]

Hello All,

Much like the two posters above me have mentioned, I narrowed the possible answer choices down to B & D. I ultimately chose B after applying the negation test, but I am still confused as to how answer choice D is considered to be "out of scope".

By negating "B" we get the statement "some other gene in the flies....is required for the formation of the UV cells" and this negated version of the original statement completely undermines argument by stating that the singular difference in cell composition is no longer enough to determine that that change leads to a lack of UV. Maybe some other cells are now required to determine whether or not a lack of UV occurs.

That much I understand.

However, doesn't AC "D" do something to a similar effect? By stating that the gene change had no effect on the flies other than UV, isn't that saying the same thing as "the gene change ONLY brings about the consequence of a lack of UV"? Doesn't this answer choice also eliminate alternative possibilities?

Is it incorrect because it does not satisfy the negation test? If we negate the statement we get "the gene change had some effect on the flies other than the lack of UV vision cells". I thought that this negated statement establishes that the gene change potentially had multiple effects on otherwise identical flies and thus undermined the connection between the premise and the conclusion.

My reasoning was: if the singular gene change had the potentiality to have multiple effects on the flies, wouldn't there be a case of causal over-determination, in which a single change in gene causes multiple events to occur. Thus making it almost impossible to accurately determine which event was actually caused. Or is the negated statement actually saying that a single change in the gene had the effect of a lack of UV IN ADDITION TO some other effects.

Sorry for the long post.

[lsatzen]

Matt Sherman's point, in regards to why D is out of scope, was something to the effect: so what if the change in gene causes some other stuff, we are only concerned with the argument core which addresses the issue of a lack of UV. So let's stick with the information in the text.

I like the simplicity of this response, but does my worry of causal over-determination bring these seemingly irrelevant "other" causes out of obscurity and into relevance? Or does my reasoning require an additional assumption that multiple effects the arise from a single cause leads to an unwanted case of causal over-determination?

[christine.defenbaugh]

It's a very interesting question that you raise, glen_oh!

Causal overdetermination is considered to be a serious problem in determining cause-effect relationships because it's a situation where many causes all have the same effect. Thus, when an effect occurs, it's impossible to accurately determine which of the various causes was THE cause that caused the effect this time!

For instance, perhaps new books, chocolate, and pu-erh tea each make me happy. When you see me, and I'm happy, it's impossible to know which of those causes is the culprit!

However, this is a slightly different situation. (D) proposes a situation where a single cause (the gene-change) has multiple effects. In this situation, those new effects don't dilute or undermine the pre-existing cause-effect relationship.

For instance, if pu-erh tea also makes me sing a little song, dance a little dance, and shout for joy, none of that changes the original idea that pu-erh tea makes me happy. We still know that's true, we've just added to it.

In other words, the addition of new effects from that cause doesn't change anything about the argued relationship between the cause and a separate effect.

I hope that helps clear things up a bit!

[jaf51200]

I'm confused with some potential gaps that I saw, but no one mentioned.

How come there is not a gap between "changed a single gene" in the premise and "damaged to this gene" in the conclusion?

Changing a gene, which results in something negative like a loss of ultraviolet vision, doesn't necessarily mean the gene was damaged. We know that the gene deals with vision, but the argument never tell us that the gene doesn't involve other characteristics. Perhaps the gene was modified to improve another characteristic (i.e. flying), which would mean that the gene was not necessarily damaged, but actually improved. How could "change" equate to "damage"? It seems like a term shift?

Additionally, is this another gap in the argument: The author assumes that ultraviolet vision can only be lost from gene damage. In other words, he assumes that ultra violet vision cannot be lost from environmental factors or physical accidents.

[WaltGrace1983]

I'm confused with some potential gaps that I saw, but no one mentioned.

How come there is not a gap between "changed a single gene" in the premise and "damaged to this gene" in the conclusion?

Changing a gene, which results in something negative like a loss of ultraviolet vision, doesn't necessarily mean the gene was damaged. We know that the gene deals with vision, but the argument never tell us that the gene doesn't involve other characteristics. Perhaps the gene was modified to improve another characteristic (i.e. flying), which would mean that the gene was not necessarily damaged, but actually improved. How could "change" equate to "damage"? It seems like a term shift?

I think what you are touching on is the whole POINT of the question. If I am not mistaken, I think your analysis is spot on!

We have two flies.

Fly A: A B C D E
Fly B: A B C D F (F is the changed gene)

Fly B doesn't have UV vision so the scientists automatically assume that it is this specific gene change or this specific damage to the gene that leads to the lack of UV Vision. But what if gene E or F is irrelevant? What if it is actually that A is damaged and that is what is causing the lack of UV Vision. In other words, the author is assuming that one gene (in this case, E) is the sole "author" of UV Vision. Without this one gene (in this case, E) then UV Vision cannot be acquired.

, is this another gap in the argument: The author assumes that ultraviolet vision can only be lost from gene damage. In other words, he assumes that ultra violet vision cannot be lost from environmental factors or physical accidents.

As for this, I think it might be a gap but its an odd one at that because it doesn't really follow from the premises too well. I think you are right to say that, "well maybe these genes are completely irrelevant and these flies just all happened to not have UV vision because they were all born at 11:45 am." Again though, it would be a pretty odd gap to attack.

I hope my analysis is correct because I have thought about this question a lot. For some reason, it just seems fairly difficult (maybe the way it is worded?)

[jaf51200]

Thanks for your very clear and concise analysis.

And I agree that its an odd gap (the genes in general as being irrelevant), but when I review questions I like to look for the smaller/less common gaps because difficult questions will sometimes involve the more obscure gap and ignore the more obvious one.

[mkd000]

Initially, my view of the flaw was that there is a shift from "changed a gene" to "damaged gene", and also: what if the gene changed so that there was some other development that made up for the lack of eye cells? Using process of elimination and the negation of possible correct answer choices, I chose (B). I still think that (B) does fit in with the aforementioned flaw I identified. Please provide feedback! (I.e., is this a misguided assessment of the argument flaw??)

In review, I noticed that another, possibly stronger/more significant flaw is the shift from a premise about damage of a gene of flies of a certain species IN AN EXPERIMENT to a conclusion about flies (lacking UV vision) of that species OUTSIDE of the experiment (i.e., those flies of that species in general). Also, in the premise, the flies with changed genes in the experiment are not stated as not have UV vision, and the assumption is that if they don't have those eye cells they don't have UV vision. The flies mentioned in the conclusion are assumed to not have those eye cells BECAUSE it is mentioned that the flies in the conclusion lack UV vision.

Am I making sense?

Thanks!!

[maryadkins]

Not sure I follow you entirely, but you're definitely in the right zone, here.

Basically, just because there is this one gene that when altered (or "damaged"—they are used interchangeably here, so that's not the flaw) causes these flies not to have UV vision doesn't mean that's the ONLY gene necessary for UV vision. This is what (B) addresses and why it is correct.

There may be 10 genes that all together are necessary for UV vision (I'm just coming up with a hypothetical, here). Take out any one of them, and the fly doesn't have UV vision anymore. The experiment did exactly this. But to conclude based on this experiment that any time a fly doesn't have UV vision, it is because this ONE gene is damaged/altered is wrong. It could have been any of the other nine! Any of THOSE being altered would have caused the fly to lose UV vision, too, because they're ALL necessary.

Hope this helps clarify!

[ChloeC62]

It's a very interesting question that you raise, glen_oh!

Causal overdetermination is considered to be a serious problem in determining cause-effect relationships because it's a situation where many causes all have the same effect. Thus, when an effect occurs, it's impossible to accurately determine which of the various causes was THE cause that caused the effect this time!

For instance, perhaps new books, chocolate, and pu-erh tea each make me happy. When you see me, and I'm happy, it's impossible to know which of those causes is the culprit!

However, this is a slightly different situation. (D) proposes a situation where a single cause (the gene-change) has multiple effects. In this situation, those new effects don't dilute or undermine the pre-existing cause-effect relationship.

For instance, if pu-erh tea also makes me sing a little song, dance a little dance, and shout for joy, none of that changes the original idea that pu-erh tea makes me happy. We still know that's true, we've just added to it.

In other words, the addition of new effects from that cause doesn't change anything about the argued relationship between the cause and a separate effect.

I hope that helps clear things up a bit!

can someone expand/clarify on this please?

is casual overdetermination happening in the stimulus? or is what she stated in D also happening in the stem?
[She states that (D) "proposes a situation where a single cause (the gene-change) has multiple effects. In this situation, those new effects don't dilute or undermine the pre-existing cause-effect relationship."]

I guess I am confused on if these two topics apply to the stem? and when they would apply? or the relevance to knowing/using these topics?