Passage Excerpt from “Research Riddle Resolved”
Excerpt from “Research Riddle Resolved”
For centuries, scientists were confounded by an animal that seemed to look and act like a combination of a bird, a reptile, and a mammal. It has a bill like a duck and lays eggs but produces milk for its young. It lives in a burrow, has fur, and can make venom. We now know that this animal is called a duck-billed platypus. A platypus is a monotreme, a type of egg-laying mammal.
Hundreds of years after the first sightings of the platypus, the animal still captures our imagination anew and irresistibly attracts the attention of science writers everywhere. The May 2008 Nature report detailing the DNA insides of the duck-billed platypus invited colorful tales from just about every mainstream media outlet.
But cuteness and weirdness aside, the platypus research results are a gold mine for medical researchers. The findings cement what may have seemed totally obvious but turned out to be a bit of a scientific surprise: platypus DNA is a patchwork of genes from reptiles, birds, and mammals.
Evolution Fusion
In other words, the platypus heritage is laid out in an evolutionary DNA tapestry that marks the time, hundreds of millions of years ago, when reptiles and mammals branched off the evolutionary tree.
So what? The platypus is nothing like a human, so what can its DNA tell us about people and the diseases we get?
Plenty, says an international team of scientists who did this work.
The platypus genome results are far more than confirmation of a scientific oddity. They provide researchers a window into a time in history when mammals became unique—gaining the ability to bear live young, produce milk for them, and grow a warm, furry coat.
That’s important because our own, modern-day genomes are still a big mystery and researchers need much more information to be able to translate our genetic language into useful health knowledge.
One of the ways scientists can decipher meaning from within our 3 billion DNA “letters,” or nucleotides, is to compare human genes with those from animals, to see what has been kept the same and what has evolved to be different. . . .
Same and Different
In an approach called comparative genomics, scientists compare the genome sequences of several species: human, mouse, and a wide variety of other organisms from single-celled fungi to elephants and, now, the platypus.
The goal of this research is to find regions of similarity and difference in order to better understand the structure and function of human genes.
Comparative genomics is directly related to evolution because all living things share a common ancestor. By using computer tools to examine genes that have been kept the same in many organisms over millions of years, researchers can locate signals that control how genes work. This information may translate into ways to understand, treat, and prevent human diseases. . . .
Chicken or Egg?
When researchers analyzed platypus DNA and compared it to that of chickens, snakes, and lizards, the findings traced the evolutionary path from birds and reptiles to mammals. They learned that the platypus lost most of its genetic ability to produce egg yolk—as compared to chicken genes. This suggests its departure from “chicken-ness.”
But, through evolutionary change, the platypus gained the ability to make milk that is rich in nutrients. Platypuses have genes that make the milk protein casein: just like we do.
A male platypus can, like its ancestral snake and lizard cousins, produce venom. The platypus ejects this venom through special glands in its back legs. The evolutionary reason for maintaining such molecular weaponry isn’t yet clear, but what is fascinating is that it appears nature mixed and matched together DNA pieces separately to create the venom genes in reptiles and monotremes like the platypus.
The scientific value of pinning genetics to physiological function—like milk production—is high. Such investigations may help medical researchers understand health issues related to reproduction and lactation. Although lactation is an ancient reproductive trait, mammals—including the platypus—are unique in their ability to produce milk that is extraordinarily nutritious, containing a rich blend of sugars, fats, and proteins.
More generally, though, studying how nature cuts and pastes gene modules gives scientists an inside scoop on how genetic changes relate to health and disease risk.
One thing is clear—the stunning blend of reptile, bird, and mammal puts the platypus in a class of its own, and it gives researchers much more: information about how mammals like us came about.
[Scientists’] genetic sleuthing of platypuses, chimps, fish, sunflowers—you name it—continues to teach scientists how millions of years of evolution progressed. This provides vital information to understanding the role of genes in the health and disease of mammals like us and our pets, and can also help preserve our rich and diverse planet.
From “Research Riddle Resolved”—Public Domain/National Institutes of Health
Question
How does paragraph 8 fit into the overall structure of the excerpt?
- AIt provides a transition from the discussion of the platypus genome to a discussion on comparative genomics.
- BIt introduces the way that scientists solved the problem of how to study complex human genomes through comparative genomics.
- CIt contrasts the efforts made to study the different parts of the human genome with the efforts made to study certain animal genomes.
- DIt elaborates on the idea that deciphering genetic signals is a rigorous research challenge.
Show the answer
Correct answer: A
The question asks how paragraph 8 fits into the overall structure of the excerpt.
A. CORRECT. Paragraph 8 acts as a transition from the discussion of how “our own, modern-day genomes are still a big mystery” (paragraph 7) to the discussion of how scientists use comparative genomics to compare “human genes with those from animals” (paragraph 8).
B. Incorrect. Paragraph 8 introduces the practice of comparing “human genes with those from animals,” but it does not clarify or provide details about how scientists solved the problem of studying complex human genomes using comparative genomics.
C. Incorrect. Rather than contrasting the effort of the study of the human genome with the effort of a separate study of animal genomes, paragraph 8 discusses a study that is comparing human and animal genomes in order “to see what has been kept the same and what has evolved to be different.”
D. Incorrect. While the mention in paragraph 8 of “3 billion DNA ‘letters’ ” certainly highlights the enormous challenge of fully analyzing the human genome, the point of paragraph 8 is to transition the excerpt to the topic of how comparative genomics can shed light on the human genome.
Question analysis
Paragraph 8 of “Research Riddle Resolved” is a single sentence about comparing human DNA with the DNA of animals, and this text-structure question asks what part it plays in the excerpt as a whole. The options describe its role in the article’s own scientific terms, so each claim has to be checked closely against what the paragraph actually does.
- Grade level
- Grade 8 reading and task
- Compared with grade 7
- At grade 7 Grade 7 readers are routinely asked what job a paragraph does in an informational text, and this question asks no more than that; the dense science writing and options phrased in general terms add some load.
- Estimated difficulty
- Moderate: several steps, or a close reading with one strong distractor.
- Thinking it demands
- Depth of knowledge 2, skills and concepts · mainly analyze
- What makes it hard
- How, not what moderate
- Evidence in several places moderate
- A very close wrong answer moderate
- Hard words minor
- Evidence
- Answered from several paragraphs or stanzas
- Reading level
- Passage: about grade 11, 809 words; question and choices: about grade 12, 84 words.
- Students, last 30 days
- Not enough answers yet to show (it takes 10).
Why it is hard, traps and wrong answers (shows the answer)
Why it is hard
Paragraph 8 sits on a hinge between a problem and a section that names a method, and two wrong choices each seize one side of it. The 3 billion DNA “letters” make the problem loom large, which draws students toward a paragraph about how hard the research is, while this printing’s version about solving the problem matches the turn toward comparative genomics but overstates it. Asking what the paragraph hands to the next section shows a transition, not a solution or a complaint.
How, not what moderate Working it out
Paragraph 8 is a single sentence that offers a method, comparing human genes with animal genes, which paragraph 9 then names “comparative genomics,” so its job is a handoff rather than a point of its own. (Anderson & Krathwohl, 2001)
Evidence in several places moderate Working it out
The paragraph’s role shows only from its neighbors: paragraph 7 calls our genomes “still a big mystery,” and the heading “Same and Different” and paragraph 9 take up the comparison it proposes. (Kirsch & Mosenthal, 1990; Gorin & Embretson, 2006)
A very close wrong answer moderate Choosing the answer
The choice about how scientists “solved the problem” also has paragraph 8 introducing comparative genomics; it parts from the key on one claim, a solution where the paragraph offers only “One of the ways.” (Embretson & Wetzel, 1987; Gorin & Embretson, 2006; Ascalon et al., 2007)
Hard words minor Understanding the question
“Decipher,” “nucleotides” and “comparative genomics,” a term that appears only in paragraph 9, stand between the student and the plain idea of comparing genes across species. (Perfetti, 2007; Freedle & Kostin, 1993)
Strategy: Decide in your own words what job paragraph 8 does for the excerpt, using what comes just before and just after it, then test each option word by word against the paragraph itself.
Traps
- Too broad or too strong: A choice overstates, generalizes, or uses absolute words the text does not support.
- Wrong purpose or structure: Names a purpose, structure or effect that the part does not serve, or describes what a part says when the question asks what it does.
- Twists what the text says: Uses the text's topic and ideas but changes what it says: who did it, how much, when, or why.
The wrong answers, classified
B Too broad or too strong (King et al., 2004)
Rightly sees paragraph 8 turning to comparative genomics but accepts that scientists “solved the problem,” though it offers only “One of the ways” to study genomes that paragraph 7 calls “a big mystery.”
C Twists what the text says (King et al., 2004)
Turns the comparison of human and animal genes, what was kept the same and what changed, into a contrast between two research efforts, which the paragraph never measures or weighs.
D Wrong purpose or structure (Anderson & Krathwohl, 2001)
Is struck by the 3 billion DNA “letters” and reads the paragraph as stressing how hard the research is, though it offers a way to meet that challenge rather than dwelling on it.
Working it out, step by step
Figure out what the question asks
This asks how paragraph 8 fits the structure of the excerpt. Structure is the way the parts are put in order. So ask what job paragraph 8 does. Look at what comes right before it and right after it.
Look at what comes before
The excerpt starts with the platypus genome. A genome is all the genes of a living thing. Paragraph 7 then turns to people. It says “our own, modern-day genomes are still a big mystery.” Researchers need more facts to turn our genes into health knowledge.
Read paragraph 8
Paragraph 8 is one sentence. It says “One of the ways scientists can decipher meaning” from our DNA “is to compare human genes with those from animals.” To decipher means to figure out what a code means. So the paragraph names one way to study our genes: compare them with animal genes.
Look at what comes after
The next section is headed “Same and Different.” Paragraph 9 gives the method a name: “comparative genomics.” Comparative means comparing. So paragraph 8 is a bridge. It leads from the platypus genome to the method the next section explains.
Check each choice
- A fits. Paragraph 8 links the platypus genome to the section on comparative genomics.
- B does not fit. Paragraph 8 gives only “One of the ways” to study our genes. Nothing says scientists have solved the problem. Paragraph 7 still calls our genomes “a big mystery.”
- C does not fit. Paragraph 8 compares genes. It doesn’t contrast the efforts of different studies.
- D does not fit. The 3 billion letters show the task is big. But the paragraph’s job is to offer a way to do it.
Choose the answer
Watch out: B is tempting because paragraph 8 does lead into comparative genomics. But B says scientists “solved the problem.” The passage offers a method, not a solution. So the answer is A.
Why this answer and not the closest wrong one
B is the closest wrong answer. Like A, it ties paragraph 8 to comparative genomics. But B claims the problem of studying human genomes was solved. Paragraph 8 offers only “One of the ways” to study them, and paragraph 7 calls them “still a big mystery.” A describes the paragraph’s real job: a bridge to the next section.
More questions like this
The original DOE question
The passage “Excerpt from “Research Riddle Resolved”” as printed (pages 66–67)
