Clone Farm

共享题干题                                               (三)
                                           Clone Farm
阅读下列的材料，回答下列问题。
         Factory farming could soon enter a new era of mass production. Companies in the US aredeveloping the technology needed to "clone" chickens on a massive scale. Once a chicken withdesirable traits has been bred or genetically engineered tens of thousands of eggs, which willhatch into identical copies, could roll off the production lines every hour. Billions of clonescould be produced each year to supply chicken farms with birds that all grow at the same rate,have the same amount of meat and taste the same.
        This, at least, is the vision of the US's National Institute of Science and Technology,which has given Origen, Therapeutics of Burlingame, California, and Embrex of North CarolinaUSD 4. 7 million to help fund research. The prospect has alarmed animal welfare groups, whofear it could increase the suffering of farm birds.
        That's unlikely to put off the poultry industry, however, which wants disease-resistant birds that grow faster on less food. "Producers would like the same meat quantity but to use reducedinputs to get there", says Mike Fitzgerald of Origen. To meet this demand, Origen aims to"create an animal that is effectively cloned", he says. Normal cloning doesn't work in birdsbecause eggs can't be removed and implanted. Instead, the company is trying to bulk-growembryonic stem cells taken from fertilized eggs as soon as they're laid. "The trick is to culturethe cells without them starting to distinguish, so they remain pluripotent", says Fitzgerald.
       Using a long-established technique, these donor ceils will then be injected into the embryoof a freshly laid, fertilized recipient egg, forming a chick that is a "chimera". Strictly speakinga chimera isn't a clone, because it contains cells from both donor and recipient. But Fitzgeraldsays it will be enough, say, 95 percent of a chicken's body develops from donor cells. "In thepoultry world, it doesn't matter if it's not 100 percent," he says.
        Another challenge for Origen is to scale up production. To do this, it has teamed up with"Embrex, which produces machines that can inject vaccines into up to 50, 000 eggs an hour.Embrex is now trying to modify the machines to locate the embryo and inject the cells intoprecisely the right spot without killing it.
       In future, Origen imagines freezing stem cells from different strains of chicken. If orderscome in for a particular strain, millions of eggs could be produced in months or even weeks. Atpresent, maintaining all the varieties the market might call for is too expensive for breeders, andit takes years to breed enough chickens to produce the billions of eggs that farmers need.