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Practice Test – 31

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This passage is adapted from Emily Anthes, Frankenstein's Cat. ©2013 by Emily Anthes.

When scientists first learned how to edit the
genomes of animals, they began to imagine all the
ways they could use this new power. Creating
brightly colored novelty pets was not a high priority.
5 Instead, most researchers envisioned far more
consequential applications, hoping to create
genetically engineered animals that saved human
lives. One enterprise is now delivering on this dream.
Welcome to the world of “pharming,” in which
10 simple genetic tweaks turn animals into living
pharmaceutical factories.
Many of the proteins that our cells crank out
naturally make for good medicine. Our bodies’ own
enzymes, hormones, clotting factors, and antibodies
15 are commonly used to treat cancer, diabetes,
autoimmune diseases, and more. The trouble is that
it’s difficult and expensive to make these compounds
on an industrial scale, and as a result, patients can
face shortages of the medicines they need. Dairy
20 animals, on the other hand, are expert protein
producers, their udders swollen with milk. So the
creation of the first transgenic animals—first mice,
then other species—in the 1980s gave scientists an
idea: What if they put the gene for a human antibody
25 or enzyme into a cow, goat, or sheep? If they put the
gene in just the right place, under the control of the
right molecular switch, maybe they could engineer
animals that produced healing human proteins in
their milk. Then doctors could collect medicine by
30 the bucketful.
Throughout the 1980s and ’90s, studies provided
proof of principle, as scientists created transgenic
mice, sheep, goats, pigs, cattle, and rabbits that did in
fact make therapeutic compounds in their milk.
35 At first, this work was merely gee-whiz, scientific
geekery, lab-bound thought experiments come true.
That all changed with ATryn, a drug produced by the
Massachusetts firm GTC Biotherapeutics. ATryn is
antithrombin, an anticoagulant that can be used to
40 prevent life-threatening blood clots. The compound,
made by our liver cells, plays a key role in keeping
our bodies clot-free. It acts as a molecular bouncer,
sidling up to clot-forming compounds and escorting
them out of the bloodstream. But as many as 1 in
45 2,000 Americans are born with a genetic mutation
that prevents them from making antithrombin.
These patients are prone to clots, especially in their
legs and lungs, and they are at elevated risk of
suffering from fatal complications during surgery
50 and childbirth. Supplemental antithrombin can
reduce this risk, and GTC decided to try to
manufacture the compound using genetically
engineered goats.
To create its special herd of goats, GTC used
55 microinjection, the same technique that produced
GloFish and AquAdvantage salmon. The company’s
scientists took the gene for human antithrombin and
injected it directly into fertilized goat eggs. Then they
implanted the eggs in the wombs of female goats.
60 When the kids were born, some of them proved to be
transgenic, the human gene nestled safely in their
cells. The researchers paired the antithrombin gene
with a promoter (which is a sequence of DNA that
controls gene activity) that is normally active in the
65 goat’s mammary glands during milk production.
When the transgenic females lactated, the promoter
turned the transgene on and the goats’ udders filled
with milk containing antithrombin. All that was left
to do was to collect the milk, and extract and purify
70 the protein. Et voilà—human medicine! And, for
GTC, liquid gold. ATryn hit the market in 2006,
becoming the world’s first transgenic animal drug.
Over the course of a year, the “milking parlors” on
GTC’s 300-acre farm in Massachusetts can collect
75 more than a kilogram of medicine from a single
animal.

The primary purpose of the passage is to

  • Solution

    Choice A is the best answer. Lines 9-11 introduce the focus of the passage: “Welcome to the world of ‘pharming,’ in which simple genetic tweaks turn animals into living pharmaceutical factories.” The passage then discusses the chronological development of “pharming,” and describes ATryn, a useful drug produced after decades of laboratory experiments.

    Choices B and C are incorrect because the passage does not primarily evaluate research or summarize long-term research findings. Choice D is incorrect because “pharming” is not a branch of scientific study.

The author’s attitude toward pharming is best described as one of

  • Solution

    Choice C is the best answer. The author is appreciative of pharming and describes it as turning “animals into living pharmaceutical factories” (lines 10-11). She expresses a positive view of pharming in line 70, when she describes its end result: “Et voilà—human medicine!”

    Choices A, B, and D are incorrect because the author’s attitude about pharming is not accurately characterized as one of fear, disinterest, or surprise.

As used in line 20, “expert” most nearly means

  • Solution

    Choice C is the best answer. In lines 19-21, the author explains that dairy animals are “expert,” or capable, “protein producers.” Choices A, B, and D are incorrect because in this context “expert” does not mean knowledgeable, professional, or trained.

What does the author suggest about the transgenic studies done in the 1980s and 1990s?

  • Solution

    Choice B is the best answer. In line 36, the author explains that the initial transgenic studies were “lab-bound thought experiments come true.” Those first studies, in other words, were considered to be of theoretical value only. They were not expected to yield products ready for human use.

    Choices A and D are incorrect because the cost of animal research and the molecular properties of certain animals are not discussed in the passage. Choice C is incorrect because the passage does not suggest that all of the transgenic studies were focused on anticoagulants.

Which choice provides the best evidence for the answer to the previous question?

  • Solution

    Choice C is the best answer. In lines 35-36, the author provides evidence that the transgenic studies done in the 1980s and 1990s were not expected to yield products ready for human use. The author explains that the initial transgenic studies were “merely gee-whiz, scientific geekery, lab-bound thought experiments come true.”

    Choices A, B, and D are incorrect because they do not provide evidence that the transgenic studies done in the 1980s and 1990s were not expected to yield products ready for human use. Choices A and B do not address the transgenic studies, and choice D focuses on ATryn, a drug that was intended for human use.

According to the passage, which of the following is true of antithrombin?

  • Solution

    Choice A is the best answer. Lines 42-44 explain that ATryn “acts as a molecular bouncer, sidling up to clot-forming compounds and escorting them out of the bloodstream.” Antithrombin can thus be seen as an agent that reduces the amount of dangerous clots in the bloodstream.

    Choices B, C, and D are incorrect because the passage does not suggest that antithrombin stems from a rare genetic mutation, is a sequence of DNA, or occurs naturally in goats’ mammary glands.

Which choice provides the best evidence for the answer to the previous question?

  • Solution

    Choice B is the best answer. Lines 42-44 provide evidence that antithrombin reduces compounds that lead to blood clots, as it acts as a “molecular bouncer, sidling up to clot-forming compounds and escorting them out of the bloodstream.”

    Choices A, C, and D do not provide evidence that antithrombin reduces compounds that lead to blood clots; these lines describe proteins, people unable to produce antithrombin, and the production of ATryn.

Which of the following does the author suggest about the “female goats” mentioned in line 59?

  • Solution

    Choice B is the best answer. In lines 60-62, the description of female goats’ kids mentions that “some of them proved to be transgenic, the human gene nestled safely in their cells.” The statement “some of them” indicates that while a number of the newborn goats were transgenic, others were not.

    Choices A, C, and D are incorrect because the passage does not suggest that the female goats used in the initial experiment secreted antithrombin in their milk after giving birth, were the first animals to receive the microinjections, or had cells that contained genes usually found in humans.

The most likely purpose of the parenthetical information in lines 63-64 is to

  • Solution

    Choice D is the best answer. In lines 63-64, the parenthetical is added after the phrase “a promoter,” which is “(. . . a sequence of DNA that controls gene activity).” The parenthetical’s purpose is to define the term “promoter.” Choices A, B, and C are incorrect because they do not correctly identify the purpose of the parenthetical information in lines 63-64.

The phrase “liquid gold” (line 71) most directly suggests that

  • Solution

    Choice D is the best answer. Gold is a valuable element that commands high prices, so calling something “liquid gold” implies that it has great value. Because the pharmaceutical company GTC was producing the drug in order to sell it, it can be inferred that describing ATryn as “liquid gold” means it proved to be a lucrative product for GTC.

    Choices A, B, and C are incorrect because the phrase “liquid gold” does not refer to the microinjection technique, efficiency in dairy production, or transgenic goats being beneficial to dairy farmers.

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