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# In an experiment, scientists changed

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In an experiment, scientists changed  [#permalink]

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20 Jun 2017, 11:17
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55% (hard)

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64% (02:03) correct 36% (02:18) wrong based on 199 sessions

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In an experiment, scientists changed a single gene in cloned flies of a certain species. These cloned flies lacked the eye cells that give flies ultraviolet vision, even though cloned siblings with unaltered, otherwise identical genes had normal vision. Thus, scientists have shown that flies of this species lacking ultraviolet vision must have some damage to this gene.

Which one of the following is an assumption required by the argument?

(A) The relationship between genes and vision in flies is well understood.
(B) No other gene in the flies in the experiment is required for the formation of the ultraviolet vision cells.
(C) Ultraviolet vision is a trait found in all species of flies.
(D) The gene change had no effect on the flies other than the lack of ultraviolet vision cells.
(E) Ultraviolet vision is an environmentally influenced trait in the species of flies in the experiment.

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Re: In an experiment, scientists changed  [#permalink]

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21 Jun 2017, 00:38
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This argument talks about an experiment, which the scientists, conducted on
a specific gene of the cloned flies. This gene, when altered showed that the
flies lacked UV vision. Hence, the scientists hypothesized that, that specific gene
was responsible for the UV vision.

An assumption which is necessary for the conclusion to stand is as follows :
"No other gene in the flies in the experiment is required for the formation
of the ultraviolet vision cells" (Option B
). If another gene was individually (or) partially
responsible for the UV vision, then the conclusion will not hold good.
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In an experiment, scientists changed  [#permalink]

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23 May 2019, 15:30
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In an experiment, scientists changed a single gene in cloned flies of a certain species. These cloned flies lacked the eye cells that give flies ultraviolet vision, even though cloned siblings with unaltered, otherwise identical genes had normal vision. Thus, scientists have shown that flies of this species lacking ultraviolet vision must have some damage to this gene.

Notes
Experiment: change 1 gene in fly —-> flies lost UV vision
Control: no change in gene —> flies got normal vision
(C) no UV vision —> gene damaged

Analysis
This is kind of like a mistaken reversal! Just because we changed one gene and it caused the flies in the experiment to lost vision, does that mean that every fly without UV vision had their genes damaged? Maybe? Not necessarily true though. It seems like the scientists assumed that that gene was solely responsible for UV vision….? Or that nothing else was responsibility…? Hm.

Which one of the following is an assumption required by the argument?

(A) The relationship between genes and vision in flies is well understood.
Well, nowhere do we need to assume the “full understanding” of the science. We just need to know whether the gene is the true culprit for UV vision loss.

(B) No other gene in the flies in the experiment is required for the formation of the ultraviolet vision cells.

Huh, sounds pretty good. Let’s negate this: Other genes are required to form UV vision cells. If gene X was changed but gene Y is also required to formed UV vision cells….then how do we know which gene was affected in the flies without UV vision capabilities? Was it X? Or Y? Therefore, if other genes are required, then this makes the scientists’ argument false. Correct!

(C) Ultraviolet vision is a trait found [color=#ed145b]in all species of flies.

Glad to know this additional premise…but “all species of flies” is too broad and way out of our stimulus subject matter!

(D) The gene change had no effect on the flies other than the lack of ultraviolet vision cells.
Hm, this also sounds good….but this answer choice gives us a little bit more about the experiment. The choice tells us that the gene only affected UV vision in the experimental fly group. OK…still kind of confused here....although it does seem like a repeat of the premise? Definitely stumped a bit here.

Let’s try negating this. Let’s say the gene also affected the flies ability to take flight AND UV vision. Does that mean that flies without UV vision definitely had this gene damaged? Not necessarily. If the gene controls other aspects, don’t both aspects have to be affected?

(E) Ultraviolet vision is an environmentally influenced trait in the species of flies in the experiment.
Not relevant. We don’t care about what influences the gene. We care about whether the lack of UV vision IS a result of the gene — not how the gene came to be.

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In an experiment, scientists changed   [#permalink] 23 May 2019, 15:30
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