Despite that, plant geneticists tend not to be overly concerned about the risks of G.M.O.s, as long as the modifications are made with some care. As a 2016 report by the National Academy of Sciences found, G.M.O.s were generally safe, though it allowed that minor impacts were theoretically possible. Fred Gould, a professor of agriculture who was chairman of the committee that prepared the 600-page report, noted that genetic changes that alter a metabolic pathway — the cellular process that transforms biochemical elements into a particular nutrient or compound — were especially important to study because they could cause cascading effects.
In practice, of course, almost everything we grow and eat today has had its DNA altered extensively. For millenniums, farmers, discovering that one version of a plant — usually a random genetic mutant — was hardier, or sweeter, or had smaller seeds, would cross it with another that, say, produced more fruit, in hopes of getting both benefits. But the process was slow. Simply changing the color of a tomato from red to yellow while preserving its other traits could take years of crossbreeding. And tomatoes are one of the easiest cases. Introducing even a minor change to a cherry through crossbreeding, I was told, could take up to 150 years.
当然,在实践中,我们如今种植和食用的几乎所有东西的DNA都发生了广泛变化。几千年来,如果农民发现一种植物的某个版本——通常是随机的基因突变——更耐寒、更甜或种子更小,他们就会将其与另一个生产更多果实的版本进行植物杂交,以期两者兼得。但这一过程很慢。仅仅将番茄的颜色从红色变为黄色,同时保留它的其他特性,可能就需要进行数年的杂交才能实现。番茄是最容易改变的作物之一。我了解到,通过杂交育种使樱桃发生哪怕是很小的变化,也可能需要长达150年的时间。
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