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RC practice Passage with Explanation -27

DNA degrades quickly after an animal dies, so researchers once believed it impossible to find ancient genetic material. The search for primeval vestiges of DNA took off in the late 1980s after the development of a technique called polymerase chain reaction (PCR), which copies minute quantities of DNA. Armed with PCR, scientists could look for tiny fragments of DNA that might have weathered the millennia unharmed.

In recent years, researchers have isolated DNA from 20—million—year—old magnolia leaves and extracted DNA from a 135—million—year—old weevil found in amber. Recently, a team extract DNA from bone dating back millions of years for the first time. In the frenzied hunt for ancient DNA, microbiologist Scott R. Woodward may have bagged the biggest quarry. Drawing on lessons learned while growing up among the fossil—rich rocks of eastern Utah, Woodward and his team became the first people to find genetic material belonging to a dinosaur.

Woodward, whose grandfather was a coal miner, knew that mines in the area often contained dinosaur traces. After six months of looking Woodward pulled two bone fragments from a Cretaceous siltstone layer directly atop a coal seam. Impeded by an unstable mine roof, Woodward's team could not recover any more bone samples. The siltstone apparently inhibited fossilization and preserved much of the original cell structure in the bone. Researchers isolated strands of DNA from both fragments and used PCR to copy a segment that codes for a protein called cytochrome b. Once they had made many copies, they could determine the DNA sequence.

Throughout their work, the biologists took precautions to avoid contaminating the samples with modern DNA or ancient material found within the coal. According to Woodward, circumstantial evidence indicates that the bone fragments belong to one or two species of dinosaurs. Dinosaur tracks are abundant in this coal formation, and the bones visible in the mine were larger than those of a crocodile—the biggest non—dinosaur known in these rocks.

Woodward explains variation found in the DNA as a result of damage to the ancient DNA, which caused the PCR technique to alter the original sequence. Scientists had hoped to use the DNA to resolve debate about the relationship among birds, dinosaurs, and other reptiles. But the cytochrome b fragments were too short to offer meaningful phylogenetic information, says Woodward. Utah's state paleontologist believes that the fragments found by Woodward could definitely be dinosaur in origin. Other researchers, however, question the identity of the DNA strands. Because the copies of the cytochrome b sequence varied considerably, they wonder whether the DNA comes from several organisms.


For which of the following statements does the passage provide some evidence or explanation?

[A] I only
[B] III only
[C] I and II
[D] II and III
Option: 1

An evaluation question. Review the main points of the passage and your map before hitting the numbers. RN I is supported in paragraph 1 by explanation and evidence. RNs II and III, however, are beyond the scope of the passage.

Wrong answers:

(B): Out of Scope. As described above.

(C): Out of Scope. As above.

(D): Out of Scope. As above.


Researchers who believe that the DNA isolated by Woodward did not come from a dinosaur would most likely use which of the following discoveries as support?

[A] Damage to the dinosaur DNA causes the PCR technique to alter the original sequence.
[B] Comparison of the discovered DNA with that of modern DNA reveals a variation in sequence.
[C] Birds, dinosaurs, and reptiles have no phylogenetic relationship.
[D] The cytochrome b sequence comprises DNA from several different animals.
Option: 4

Where would you find doubters of Woodward's analysis? Check the last paragraph. The main objection to the idea that Woodward's DNA came from a dinosaur is that variation in cytochrome b sequences might indicate multiple animal DNA. (D) simply states this objection as evidence.

Wrong answers:

(A): Out of Scope. This wouldn't necessarily indicate that the DNA isn't of dinosaur origin.

(B): Out of Scope. This would be expected of dinosaur DNA and might even support Woodward a bit.

(C): Out of Scope. The fundamental objection to Woodward's analysis would still be unsupported further even if this were true. This is something scientists hoped to resolve as a result of Woodward's evidence, not a test they were using to determine the truth of his theory.


According to information put forth and argued by the author in the passage cytochrome b was useful to the scientists because:

[A] it provided the scientists with a DNA template that could be studied.
[B] once broken into fragments, it provided the scientists with much phylogenetic information.
[C] after careful study of copies of the cytochrome b, scientists were able to assign its origin to one specific dinosaur.
[D] it allowed the scientists to realize that the DNA belonged to a dinosaur rather than a crocodile.
Option: 1

Go back to the mechanism—of—action section of paragraph 3 to review. Cytochrome b was useful to the scientists because they could use it to make copies of the DNA fragment and then sequence it. (A) repeats this.

Wrong answers:

(B): Opposite. Woodward himself says in the last paragraph that this wasn't the case.

(C): Opposite. Woodward suggests in paragraph 4 that the DNA probably came from either one or two species of dinosaur.

(D): Faulty Use of Detail. The scientists believed that it was a dinosaur because of the large bones, not because of any DNA evidence.

Strategy Point: It's not necessary to know every detail of a scientific process in the Verbal section. Even knowing the broad point of a piece of evidence or certain test will be enough to answer any questions that test you on it.


Considering the passage and its various points, which of the following statements explains why Woodward's research distinguishes itself from earlier research?

[A] Results from Woodward's experimentation finally clarified the evolutionary relationship between birds, dinosaurs, and reptiles.
[B] Woodward was the first researcher to extract ancient DNA from fossils.
[C] Prior to Woodward, researchers were unable to use PCR effectively in the recovery of ancient DNA.
[D] Previous researchers had only been able to extract ancient DNA from plants and insects.
Option: 4

What is the author's main point for writing about Woodward? It represents the first time that DNA of any sort had been isolated from a dinosaur. (D) says the same thing another way.

Wrong answers:

(A): Opposite. Paragraph 5 points out that it doesn't.

(B): Opposite. Paragraph 2 gives examples of previous extractions.

(C): Out of Scope. The author doesn't give any indication that this is true.


Based on the author's claims and arguments made in the passage, the author would agree with all of the following statements EXCEPT:

[A] Utah provides paleontologists with ample opportunity to study fossils.
[B] siltstone encouraged fossilization thereby maintaining the structure of the dinosaur DNA.
[C] hazardous working conditions kept Woodward's team from continuing their search.
[D] PCR allows researchers to study quantities of DNA that once were considered too small for accurate research.
Option: 2

Briefly sum the author's main ideas: Woodward was the first to isolate dinosaur DNA, but it wasn't a large enough sample to provide detailed information about a species. Scanning the answers shows choices focused more on detail, however. Look for a detail that runs counter to the author's descriptions, or eliminate the ones that fit in. (B) is the opposite of what the author says in the middle of paragraph 3: the siltstone inhibited fossilization.

Wrong answers:

(A): Opposite. The author mentions this in paragraph 2.

(C): Opposite. This is mentioned in paragraph 3.

(D): Opposite. The author makes this point in paragraphs 1 and 3.


The passage suggests that researchers continue to look for dinosaur DNA because:

[A] the DNA found by Woodward derived from several different species.
[B] the amount of DNA retrieved was too small to copy using PCR.
[C] the DNA fragments produced by PCR were too insignificant to determine substantial information about bird, dinosaur, and reptile phylogeny.
[D] the sites where Woodward excavated had never been highly populated with dinosaurs.
Option: 3

Where is a possible use of dinosaur DNA mentioned? Review paragraph 5: scientists wanted dinosaur DNA to figure out how dinosaurs, birds, and reptiles fit together. They continue to look because Woodward's sample wasn't enough. (C) summarizes these points.

Wrong answers:

(A): Faulty Use of Detail. While this is mentioned in paragraphs 4 and 5, it isn't a motivation for continuing the search.

(B): Opposite. The passage suggests that PCR was successful in copying the DNA.

(D): Opposite. Evidence to the contrary is given in paragraph 4.


The phrase "bagged the biggest quarry " refers to Woodward's:

[A] development of a technique called polymerase chain reaction, which allows researchers to copy minute fragments of DNA.
[B] extensive research into the phylogeny of reptiles and dinosaurs.
[C] discovery of a method for extracting ancient DNA from fossils.
[D] isolation of DNA from dinosaur bone.
Option: 4

Go back to review the phrase in context. The author suggests that Woodward's snagged the best sample of ancient DNA so far. Only one answer choice, (D), has to do with discovery of physical samples at all, and fits with what Woodward did.

Wrong answers:

(A): Faulty Use of Detail. Woodward used PCR technique, he didn't develop it.

(B): Faulty Use of Detail. This is listed as a potential benefit of the discovery of dinosaur DNA.

(C): Out of Scope. Again, Woodward used the PCR technique which was already invented.


The findings of Woodward are by no means universally accepted. Which of the following findings, if true, would MOST contradict the researchers who question the identity of Woodward's dinosaur DNA?

[A] Variations in the cytochrome b sequence of Woodward's DNA have been directly linked to hybrid DNA.
[B] Carbon dating proved that the bone fragments retrieved by Woodward were from the Cretaceous era.
[C] More elaborate PCR traced the cytochrome b sequence in Woodward's sample to one species of dinosaur.
[D] Utah's state paleontologist confirmed that dinosaurs were abundant in the areas where the researchers excavated.
Option: 3

Review the main points of the researchers voicing objections in paragraph 5. Their primary objection is that the DNA may have come from more than one species. Look for an answer choice that would weaken this. (C) would put this particular objection to rest immediately.

Wrong answers:

(A): Opposite. This would bolster objections, supporting the many—species theory.

(B): Out of Scope. This would be irrelevant to the objections.

(D): Out of Scope. This part of the theory isn't being challenged.

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