LSAT Explanation PT 41, S1, Q10: In an experiment, scientists changed a

LSAT Question Stem

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

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

Let's begin by analyzing the argument in the passage. The scientists conducted an experiment where they altered a single gene in cloned flies. The result was that these flies lacked ultraviolet (UV) vision, while their unaltered cloned siblings had normal vision. The conclusion drawn from this experiment is that flies of this species lacking UV vision must have damage to this gene.

The structure of the argument can be broken down as follows:

1. Premise: Altered gene in cloned flies resulted in lack of UV vision.

2. Premise: Unaltered cloned siblings had normal vision.

3. Conclusion: Flies lacking UV vision must have damage to this gene.

To make this more understandable, let's use a simple analogy. Imagine you have two identical cars, and you remove the battery from one of them. The car without the battery won't start, while the other car starts normally. You then conclude that if a car doesn't start, it must have a problem with its battery.

The question type for this problem is Necessary Assumption. We need to identify an assumption required by the argument.

An "Evaluate" question for this argument could be: "Are there any other genes or factors that could affect the development of UV vision in these flies?"

Now, let's examine each answer choice:

a) The relationship between genes and vision in flies is well understood.

- While some understanding of this relationship might be necessary, it's not required that it is well understood. This answer choice is incorrect.

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

- This is the correct answer choice. For the conclusion to hold, the argument assumes that the altered gene is the only gene required for the formation of UV vision cells. If there were other genes involved, the lack of UV vision could be due to damage to any of those genes, not just the one altered in the experiment.

c) Ultraviolet vision is a trait found in all species of flies.

- This is not a necessary assumption. The argument only needs to focus on the species of flies used in the experiment. This answer choice is incorrect.

d) The gene change had no effect on the flies other than the lack of ultraviolet vision cells.

- This is irrelevant to the conclusion. Even if there were other effects, it doesn't undermine the conclusion that flies lacking UV vision must have damage to the gene. This answer choice is incorrect.

e) Ultraviolet vision is an environmentally influenced trait in the species of flies in the experiment.

- If UV vision were environmentally influenced, the lack of UV vision might not be related to the flies' genetic makeup. This would weaken the argument, making this answer choice incorrect.

In summary, the correct answer choice is (b), as it is a necessary assumption for the conclusion that flies lacking UV vision must have damage to the specific gene altered in the experiment.