SAT Reading Practice Test 4

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 10simple 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 1980's 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. A Tryn is antithrombin, an anticoagulant that can be used to 40prevent 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 452,000 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 50and 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 55micro injection, the same technique that producedGloFish and Aqu Advantage 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 betransgenic, 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, forGTC, 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” onGTC’s 300-acre farm in Massachusetts can collect 75 more than a kilogram of medicine from a single animal.