Reading ComprehensionDifficulty: Hard

PT145 S1 P4 Q26 Explanation

Genetic Typos

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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

Strengthen

Your task

Find the choice that makes the argument's conclusion more likely to be true.

Common trap

Answers that are consistent with the argument but add no real support, or that strengthen a claim the argument doesn't make.

Winning move

Locate the gap between evidence and conclusion, then pick the choice that closes it.

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

The question
26.

Which one of the following, if true, would most strengthen the position attributed to Steele and his colleagues

Answer choices

  1. Correct61% picked this

    Scientists have succeeded in altering the DNA in reproductive cells of laboratory mice by introducing a

    Why this is right

    This buttresses the claims being made in the 3rd paragraph by "Steele and company". They believe it's possible for a virus to transport altered DNA into the reproductive DNA. This answer gives us an example of a virus carrying new DNA to reproductive cells and changing them! It looks like they were right. It is possible.

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

  2. Out of Scope: nervous system6% picked this

    The patterns of mutations found in the genes that carry instructions for immune system responses are also found in

    Steele and colleagues didn't make any claims about the nervous system. It's not clear why the "signature" pattern of mutations appearing in the nervous system makes it any more likely that this pattern indicates that DNA has been transferred into reproductive organs.

  3. No Impact2% picked this

    The process by which the immune system tests out the efficacy of cellular mutations is one of

    We were already assuming it was trial and error, since mutations don't have any intelligence or goal-oriented behavior. So, this barely feels like new information, and it doesn't help us believe that viruses can transmit altered DNA into reproductive DNA, or that the "signature" pattern of mutations in immune system genes means that in the past DNA has been transferred to the reproductive organs.

  4. No Impact4% picked this

    Fossil remains show that giraffes gradually evolved with increasingly

    We know that giraffes gradually evolved with long necks. The Lamarckian explanation is that "by stretching during their lifetimes, they elongated their necks and passed on that trait to their offspring". The accepted Darwinian explanation is that "the giraffes with longer necks were more likely to survive and have babies, so the trait of longer necks was naturally selected for". The fact that giraffes have long necks doesn't answer the question of how they evolved those long necks.

  5. Yolk Sac vs. DNA26% picked this

    It is known that birds can pass on acquired immunities to their gestating chicks via the yolk

    This is very close to usable, but Steele & Co. are trying to establish that you can pass on acquired immunities to reproductive DNA. A chick gestating in a yolk sac is similar to a fetus gestating in a mother's womb. Both the chick and the fetus already have their DNA at the point they're gestating. Moms pass on acquired immunities via their placenta and via their breastmilk (once the babies are born). That's not the same as the kid having DNA that was changed by the mom acquiring an immunity. The kid is picking up antibodies from the placenta. The chick is picking up antibodies from the yolk sac. But Steele & Co are positing that the kid / chick could actually be picking up acquired immunities via their DNA.

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