Chimeras Read Theory Answers -

Passage

The word "chimera" originally stems from Greek mythology. In these ancient stories, the Chimera was a fearsome beast, typically depicted as a hybrid creature with the body of a lion, the head of a goat arising from its back, and a tail that ended in a snake's head. This terrifying monster was eventually slain by the hero Bellerophon. For centuries, the term was used to describe something impossible, a figment of the imagination, or a foolish fancy.

However, in the modern world, the term has taken on a new, scientific reality. In biology, a chimera is an organism composed of cells with more than one distinct genotype. Unlike a hybrid—such as a mule, which is the offspring of a donkey and a horse and has a uniform mix of DNA from both parents—a chimera actually possesses two different sets of DNA. This can occur naturally or be artificially induced.

The most common form of natural chimerism in humans occurs during pregnancy. In a phenomenon known as "vanishing twin syndrome," a fetus absorbs the cells of its twin in the early stages of development. As a result, the surviving individual may have a mix of their own DNA and their twin’s DNA. This can lead to fascinating and sometimes confusing medical situations, such as a person having two different blood types or skin pigmentation patterns. There have been documented cases where a person’s DNA does not match their children’s because the DNA tested came from a "vanished twin" rather than the cells responsible for reproduction.

Scientific advancements have also allowed researchers to create chimeras in laboratories. By introducing human stem cells into animal embryos, scientists hope to grow human organs inside animals for transplantation. While this field holds immense promise for saving lives, it also raises significant ethical questions regarding the boundaries between humans and animals.

Questions

1. According to the text, what is the primary difference between a hybrid and a chimera? A. A hybrid is mythical, while a chimera is real. B. A hybrid has a uniform mix of DNA from two parents, whereas a chimera has two distinct sets of DNA. C. A hybrid can only occur in animals, while a chimera can only occur in humans. D. A hybrid has two distinct sets of DNA, whereas a chimera has a uniform mix.

2. The author uses the example of "vanishing twin syndrome" to illustrate: A. How myths can influence modern science. B. A way in which natural chimerism occurs in humans. C. The dangers of laboratory-created chimeras. D. Why the Chimera of Greek mythology was feared. chimeras read theory answers

3. As used in paragraph 3, the word "distinct" most nearly means: A. Distinguishable B. Blurred C. Similar D. Impossible

4. Based on the passage, which of the following situations would be an example of chimerism? A. A mule born with the strength of a horse and the endurance of a donkey. B. A person whose blood type is Type A, but whose hair follicles contain Type B DNA. C. A scientist creating a new medicine using stem cells. D. A lion hunting a gazelle in the wild.

5. The passage suggests that laboratory-created chimeras: A. Are currently illegal in all countries. B. Are impossible to create with modern technology. C. Offer potential medical benefits but also present ethical dilemmas. D. Are the same as the mythical Chimera described by the Greeks.

Answer Key & Explanations

1. B Explanation: Paragraph 2 explicitly distinguishes the two. A hybrid (like a mule) has a "uniform mix of DNA," while a chimera "possesses two different sets of DNA."

2. B Explanation: Paragraph 3 introduces "vanishing twin syndrome" immediately after stating that natural chimerism occurs. It describes the mechanism of a fetus absorbing a twin, resulting in two sets of DNA, which is a direct example of natural human chimerism.

3. A Explanation: In this context, "distinct" refers to genotypes that are different or distinguishable from one another. The passage contrasts them to show they are separate sets of DNA. Passage The word "chimera" originally stems from Greek

4. B Explanation: This is the only option

Answer: To explain how the meaning of the word "chimera" has evolved from mythology to science and to discuss the ethical implications of biological chimeras.

Explanation: The passage does not simply define "chimera." It traces the term’s journey. The myth provides the metaphor, but the main focus is the scientific definition and its consequences. Distractors like "to describe the Greek monster in detail" are too narrow.

If you encounter a different set of questions, use these evidence-based strategies:

Answer: Present from birth.

Explanation: In the context of a fraternal twin absorption, the condition is not a disease you catch but a developmental event in utero. Read Theory often adds this vocabulary question. "Contagious," "surgical," and "psychological" are incorrect.