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In everyday conversation, cloning is often imagined as producing a carbon-copy of an entire organism. Biologists, however, use the term more broadly to describe making genetically identical copies at different scales—genes, cells, tissues, and, in rare cases, whole organisms. This umbrella meaning matters because the word gathers together methods that differ sharply in technical steps, aims, and ethical implications.
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One of the earliest approaches to organismal cloning is embryo splitting, sometimes called twinning. In this procedure, an early embryo at the stage of only a few cells is mechanically divided so that each half can continue developing on its own. The result is analogous to naturally occurring identical twins: two embryos with the same nuclear DNA, both derived from a single fertilized egg. The method does not involve replacing DNA or re-engineering cells; it simply separates developmental potential that was already present. Because it relies on a fertilized egg, embryo splitting is best viewed as a refinement of assisted reproduction rather than a radical departure from it.
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More technically demanding is somatic cell nuclear transfer (SCNT), the technique that produced the sheep Dolly in the 1990s. SCNT begins with an unfertilized egg cell from which the nucleus—containing almost all the cell’s DNA—has been removed. The emptied egg then receives a nucleus from a somatic (body) cell taken from an animal that one hopes to clone. If the reconstructed egg is coaxed to begin dividing, it forms an embryo carrying the donor’s nuclear genome. Unlike embryo splitting, SCNT uses DNA from a mature cell that has long since committed to a specialized identity. Reverting that nucleus to an embryonic state is biologically formidable because the pattern of chemical marks that control gene activity—the epigenetic landscape—must be widely reset. Failures in this reprogramming help explain why SCNT remains inefficient, with many embryos failing to implant or develop normally.
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A third path, sometimes mentioned alongside cloning but distinct in goal, is the generation of induced pluripotent stem cells (iPSCs). Here, researchers reprogram an adult cell back to a flexible, embryonic-like state by altering the expression of a handful of regulatory genes. iPSCs can be expanded into many kinds of tissues genetically matched to the donor. Unlike SCNT, the aim is not to produce an embryo for reproduction but to generate patient-specific cells for research or potential therapy. For that reason, iPSC work is often described as a “cloning” of cellular potential rather than an attempt at making a copy of an entire organism.
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Cloning’s conceptual boundaries become clearer when we look at organisms that reproduce asexually in nature. Many plants, some invertebrates, and a few vertebrates can generate near-identical offspring from cuttings, budding, or parthenogenesis. In agriculture and horticulture, humans harness this clonal capacity through vegetative propagation and micropropagation, producing uniform crops or disease-free stock. These examples remind us that cloning is not solely a laboratory invention; it also names a spectrum of strategies by which life repeats successful genetic combinations.
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Despite their shared label, these methods diverge in their ethical and practical profiles. Embryo splitting stays closest to conventional reproduction, yet it raises questions about the number and disposition of embryos. SCNT carries the scientific promise of copying genotypes valuable for conservation or agriculture, but its low success rates and risks of abnormal development make it controversial, especially in mammals. iPSC technology sidesteps the creation of embryos, thereby avoiding some objections, but it introduces others—such as how to regulate embryo-like structures that iPSCs can form under certain conditions. Across all methods, debates concentrate on welfare considerations, the moral status of early developmental stages, and whether the benefits justify the risks.
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Because language shapes policy, it is important to distinguish the techniques rather than treat them as interchangeable. When “cloning” is used without qualification, the public may assume that any laboratory work aims to produce a copy of a person or animal. In practice, most contemporary research focuses on cellular models and tissues that never approach reproduction. Clear terminology helps reconcile scientific goals with social expectations and legal rules.
Questions:
1. According to paragraph 2, what is a defining feature of embryo splitting? [Detail]
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2. The word “analogous” in paragraph 2 is closest in meaning to: [Vocabulary]
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3. Which of the following is NOT mentioned as a difficulty associated with SCNT? [Negative Factual]
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4. In paragraph 3, the phrase “epigenetic landscape” refers to: [Detail]
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5. What is the primary goal of iPSC technology as described in paragraph 4? [Detail]
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6. Why does the author discuss asexual reproduction in plants and some animals in paragraph 5? [Purpose]
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7. Which of the following best describes the organization of paragraph 6? [Rhetorical Purpose]
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8. The word “interchangeable” in paragraph 7 is closest in meaning to: [Vocabulary]
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9. In the paragraph below, indicate where the following sentence best fits.
This widespread assumption can distort public debate and complicate regulation. [Sentence Insertion]
Because language shapes policy, it is important to distinguish the techniques rather than treat them as interchangeable. (A) When “cloning” is used without qualification, the public may assume that any laboratory work aims to produce a copy of a person or animal. (B) In practice, most contemporary research focuses on cellular models and tissues that never approach reproduction. (C) Clear terminology helps reconcile scientific goals with social expectations and legal rules. (D)
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10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by dragging the letters of the three answer choices that express the most important ideas into the box. Put them in the alphabetical order[Summary]
Cloning encompasses multiple methods with distinct goals, challenges, and ethical profiles.
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Total Questions: 0
Incorrect Answers: 0
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