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# DNA degrades quickly after an animal dies, so researchers once

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Tuck School Moderator
Joined: 31 Aug 2016
Posts: 288
GMAT 1: 700 Q49 V37

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15 Oct 2018, 08:09
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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 palaeontologist 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.

1. 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.

E. DNA cannot survive for such long periods of time

2. 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.

E. they were hoping they might chance upon the DNA of a different dinosaur

3. 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 palaeontologist confirmed that dinosaurs were abundant in the areas where the researchers excavated.
E. An independent study reported that the DNA discovered by Woodward in fact belongs to a hen

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Re: DNA degrades quickly after an animal dies, so researchers once  [#permalink]

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26 Oct 2018, 21:54

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Re: DNA degrades quickly after an animal dies, so researchers once  [#permalink]

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27 Oct 2018, 04:41
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Q1. 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?

D. The cytochrome b sequence comprises DNA from several different animals.
Correct, text reference: '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.'

Q2. The passage suggests that researchers continue to look for dinosaur DNA because:

C. the DNA fragments produced by PCR were too insignificant to determine substantial information about bird, dinosaur, and reptile phylogeny.
Correct, text reference: '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.'

Q3. 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?

C. More elaborate PCR traced the cytochrome b sequence in Woodward‘s sample to one species of dinosaur.
Correct, text reference: 'According to Woodward, circumstantial evidence indicates that the bone fragments belong to one or two species of dinosaurs.'
So, if more evidence is presented to confirm that the sample belonged to one of the species of dinosaur then it would strengthen Woodward's claim and hence would contradict other researchers claim.
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Re: DNA degrades quickly after an animal dies, so researchers once   [#permalink] 27 Oct 2018, 04:41
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