New SAT Reading Practice Test 31

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.