Logical Reasoning

PT3 · S2 · Q23 “DNA fingerprinting” is a recently-introduced

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“DNA fingerprinting” is a recently-introduced biochemical procedure that uses a pattern derived from a person’s genetic material to match a suspect’s genetic material against that of a specimen from a crime scene.

Conclusion

The odds against a DNA fingerprint matching by chance alone are astronomically high.

Evidence

They assume that the different characteristics in a single pattern (derived from a person's genetic material) are independent of one another.

Evaluate

The premise is a little hard for me to understand. They're deriving a pattern from a person's genetic material. That pattern apparently can represent multiple different characteristics. What are these characteristics?

Are they saying a pattern might include, like, "the genes for blue eyes and brown hair?" If so, then the assumption is that the genes for blue eyes are independent of the ones for brown hair. If that assumption were wrong, it might be more like

Why do we care about whether they're independent or not? It's not clear, but our common sense would probably guess that the more independent features the pattern captures, the less likely it would be for someone else to have the same match.

Ultimately, we might not need to care about the confusing assumption. The question stem is just asking for us to weaken the claim, which was that

Goal

Let's look for an answer that helps us argue that

23.

Which one of the following, if true, casts the most doubt on the claim of the proponents of DNA fingerprinting?

The large amount of genetic
No Impact
Excluding the genetic material everyone shares is what a sensible procedure would do, since shared material could never distinguish one person from another. Filtering out the stuff we all have in common makes it less likely that two different people would have a matching pattern, so if anything this strengthens.
9% picked this
There is a generally accepted
Opposite
An accepted theoretical basis for reading the patterns lends the procedure credibility. It supports the proponents rather than casting doubt on their odds. If the way the patterns were interpreted were more subjective, it would create the sort of messiness that would help us argue that there could be false positive matches between two different people's samples.
3% picked this
Correct
In the whole population there
Why this is right
Even if we don't fully understand this answer, the fact that it's saying that people belonging to the same subgroup would have certain shared sets of genetic characteristics means that it's our best available option for arguing that two different people might have a matching pattern. We can argue that the odds of a false match aren't astronomically high, if the two people both belong to the same subgroup, since those two people would share certain sets of genetic characteristics and thus have somewhat similar patterns. The answer seems to undermine the assumption in the final sentence, implying something like the idea that "blue eyes + brown hair" wouldn't be two independent characteristics, but rather one set.
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
79% picked this
The skill required of laboratory
No Impact
We might think this weakens, by making the technique sound unsophisticated (not much skill is required to do it? pssh, sounds basic) But it could also strengthen, by making the technique sound like it can be correctly replicated by different lab techs (they don't need some sort of extraordinary skill to do it correctly). There isn't really a common sense link one way or the other between the skill of using a tool and the efficacy of a tool. Firearms are pretty simple to use, but that doesn't make them ineffective as a tool.
1% picked this
In the investigation of certain
Opposite
Successfully tracing diseases through large families makes it sound like the technique is pretty badass. It shows the techniques work, even within the similar genetic pool of a family, which if anything supports the proponents.
7% picked this

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