In an experiment, scientists changed

Answer choices

1. A

   Too Strong: well understood3% picked this

   The relationship between genes and vision in flies is

   If we negate this and say that the relationship is only partially understood, does that weaken the argument? Not really. We definitely understand that changing this single gene in this species of fly causes there to be no UV vision, because we have a perfect control group (cloned sibling with unaltered, otherwise identical genes) who didn't lose their UV vision. For the sake of this argument, that's all the author needs to assume we understand well.

   3%
2. B

   Correct73% picked this

   No other gene in the flies in the experiment is required for the formation of

   Why this is right

   This has the lovable ruling-out "not / no" that is in so many correct Necessary Assumption answers. We think of this style of wording as an invitation to use the Negation Test. If we negate this and say that "there are other genes for this species of fly that are required for the formation of the UV cells", does that weaken? Yes! It points to an alternate way that a fly of this species could lose its UV vision. Let's say that all the genes from gene 80 to gene 85 are required for the formation of UV cells. Researchers found that when they changed gene 82, the fly no longer had UV vision, and the author concludes that any time we see a fly of this species lacking UV vision, it must have some damage to gene 82. But the negation of this answer is saying that changing gene 80, or 81, or 83 / 84 / 85 would have also caused the fly to lose UV cells. So if we see a fly of this species that lacks UV vision, we can't be sure it has a damaged gene 82. It might have a damaged gene 80 instead. We didn't know what specific alternate explanation they would give us, but we anticipated that the way to hurt this argument was to say there could be some other way that a fly of this species would end up with no UV vision, and thus we can't act like "damage to this gene" is the only possible cause.

   Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

   73%
3. C

   Too Strong: all8% picked this

   Ultraviolet vision is a trait found in all species

   The author doesn't need to assume that UV is a trait found in any other species of fly besides the one the argument is about. She certainly doesn't need to assume it's present in 100% of flies. Would it change her argument if we negated this and said, "Hey, author -- UV vision is only found in 99% of flies"? Of course not. Her conclusion isn't about flies in general; it's only about "flies of this species".

   8%
4. D

   Too Strong: no other effects14% picked this

   The gene change had no effect on the flies other than the lack of

   This also has the lovable ruling-out "not / no" format, so let's negate. Does it hurt the argument if we say, "Hey, author -- the gene change also gave the flies weird smelling breath / or, it changed the rate at which their wings flap / or, it made them more susceptible to fly acne." The author doesn't care. Her logic is only concerned with the fact that we know changing this gene did take away the UV vision. Her conclusion is trying to reason backwards from a fly with no UV vision. Other effects wouldn't have any impact on the conversation.

   14%
5. E

   Weakens3% picked this

   Ultraviolet vision is an environmentally influenced trait in the species of flies

   The author needs to assume that UV vision is not an environmentally influenced trait. If it is environmentally influenced trait, then there could be alternate explanations for why a fly of this species lacks UV vision. We might look at such a fly and think, "Maybe it had damage to gene 82, like in the experiment. But ... maybe it lost its UV vision from some environmental factor, like eating a poisonous toxin."

   3%