LSAT 122 | Section 1 | Logical Reasoning: Q10

LR Question 10 Explanation

QUESTION TEXT: In an experiment, scientists changed a single gene in cloned flies…

QUESTION TYPE: Necessary Assumption

CONCLUSION: Flies lacking ultraviolet vision must have damage to the gene identified by the scientists.

REASONING: Flies with damage to the gene lack ultraviolet vision.

ANALYSIS: The scientific language is a mouthful, but this question makes a pretty simple logical error. It incorrectly reversed the premise.

Lack of the gene causes lack of vision, but lack of vision doesn’t necessarily result from lack of that particular gene. Different causes can produce the same effect. A necessary assumption will eliminate some of the other possibilities.

___________

1. Even if we didn’t understand it well, this doesn’t undermine the argument’s evidence that the flies lack ultraviolet vision when the gene as missing.
2. CORRECT. This prevents other genes from serving as alternate causes, and the assumption is necessary for the argument’s conclusion to be correct.
3. Not necessary. It is only a requirement that ultraviolet vision be present in all individuals within this particular species of fly.
4. It’s possible it has other effects, but the argument only concerns itself with identifying the cause of the loss of ultraviolet vision.
5. This would actually weaken the argument, as it is assuming ultraviolet vision is always genetic and not environmental.

Recap: The question begins with “In an experiment, scientists changed a single gene in cloned flies”. It is a Necessary Assumption question. Learn more about LSAT Necessary questions in our guide to LSAT Logical Reasoning question types.