Reading ComprehensionDifficulty: Medium

PT145 S1 P4 Q21 Explanation

Genetic Typos

A free, expert breakdown of this official LSAT Reading Comprehension question.

TopicsLocal PurposeScience

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Passage

The French biologist Jean-Baptiste de Lamarck (1744–1829) outlined a theory of evolutionary change in 1809, 50 years before Darwin’s On the Origin of Species. Lamarck’s basic idea was that organisms change in adapting to their environment and then pass on to their offspring the new characteristics they have acquired. Since then, Lamarck his colleagues claim to have found evidence for a Lamarckian hereditary mechanism in the immune system.

The immune system is an evolutionary puzzle in its own right: How is it that our bodies can quickly respond to so many different kinds of attacks? Is all this information in the genes? If so, then how does our immune system defend against new diseases? Part of the answer comes from the immune system to test out different defenses until it finds one that does the job.

Steele hypothesizes that the altered RNA then reverts back into DNA. Indeed, such “reverse transcription” of RNA back into DNA has been observed frequently in other contexts. But the troublesome question for Lamarckians is this: Could this new DNA then be carried to the reproductive genes (in the sperm and egg cells), could carry the altered DNA to the reproductive cells and replace the DNA in those cells.

But even if the process Steele and his colleagues describe is possible, does it ever actually occur? Evolutionary mechanisms are never observed directly, so we must make do with circumstantial evidence. Steele and his colleagues claim to have found such evidence, namely a “signature” of past events that is “written all over” suggest there may be other, less radical explanations for the pattern of mutations that Steele cites.

What this question is testing

Local Purpose

Your task

Identify why the author included the referenced detail at that point in the passage — its function, not its content.

Common trap

Answers that merely repeat or summarize the topic of the detail instead of describing the role it plays.

Winning move

Ask what job the detail does for the paragraph, then for the passage's broader point.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
21.

The author most likely calls a certain kind of mutation a “typo” (second paragraph) primarily

Answer choices

  1. Wrong Purpose: distinguish from adaptive13% picked this

    distinguish it from mutations that are

    All mutations are random, and we designate them as "adaptive" if they have survival value for the organism in that organism's environment. It sounds like some of these typos end up being the right fit to "do the job" against a novel disease, so those typos would be adaptive mutations.

  2. Opposite, if anything: inconsequential6% picked this

    characterize it as relatively

    While a "typo" in an email might be an inconsequential mistake, the passage is suggesting the opposite here. Some of these genetic typos are allowing the immune system to craft an effective defense against a new disease. That sounds like a pretty consequential typo!

  3. Correct75% picked this

    indicate that it is an instance of

    Why this is right

    This answer seems to obvious and literal that it feels dangerous to pick it, but it's definitely accurate. A cell's DNA is being transcribed into RNA (i.e. copied onto a different medium) but a mutation is causing an imperfect copy. The variation caused by the imperfect copying is how the immune system can "learn" to fight a new disease it didn't already have "knowledge" of, coded in its genes.

    Skill tested: Local Purpose · how this choice captures the passage's function is the move to repeat next time.

  4. Not Emphasized: easily overlooked2% picked this

    emphasize that it is easily

    While a "typo" in an email might be easily overlooked, the author isn't stressing any such thing here. The author is explaining how the immune system can defend against new diseases.

  5. Dictionary Trap3% picked this

    suggest an analogy between scientific investigation and

    This is playing too literally off the traditional sense of "typo", when we're writing or typing something. Nothing in the passage is discussing "textual analysis", or proposing that scientific investigation is similar to analyzing texts. The author is only talking about "typos" because she's explaining how mutations allow the immune system to deal with new diseases.

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