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
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.
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.
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.
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.
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.
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.
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.