LSAT 3 | Section 2 | Logical Reasoning: Q23

LR Question 23 Explanation

QUESTION TEXT: “DNA fingerprinting” is a recently-introduced biochemical…

QUESTION TYPE: Weaken

CONCLUSION: There are very low odds of obtaining a DNA match by chance alone: DNA fingerprinting is likely to be reliable.

REASONING: The odds are based on the assumption that there is independence between the different characteristics in a single pattern. (This means that if we have brown hair, it doesn’t change the odds of us having brown eyes vs. blue eyes. It is not a good assumption. )

ANALYSIS: We all know that many groups such as families share a lot of genetic material. There is no independence between genetic traits in these groups. For example, if you know I have my mother’s hair and am related to her, it is more likely that I will also have the same eye color. This increases the chance that DNA fingerprinting could lead to false matches.

On a question like this, it’s alright to ignore the complex language and think about the situation using common sense. They are claiming that DNA matching rarely produces errors. Try to think of something that could produce errors. If groups share DNA, that could produce errors.

___________

1. This strengthens the argument. Only unique genetic material is used for fingerprinting.
2. This also strengthens the argument: there is a reliable method for judging the results.
3. CORRECT. If different groups share genetic material that could cause a false match. An individual could be accused of having been at the crime scene when really it was just someone else from the same sub-group.
4. This decreases the likelihood that lab technicians will make mistakes.
5. This helps show that DNA fingerprinting is a useful technique.

Recap: The question begins with “”DNA fingerprinting” is a recently-introduced biochemical”. It is a Weaken question. Learn how to master LSAT Weaken questions on the LSAT Logical Reasoning question types page.