After a long struggle, researchers have finally cloned the rat, a longtime laboratory favorite used to study high blood pressure, diabetes, brain diseases, and many other human illnesses. The accomplishment sets the stage for the creation of genetically engineered rats that can serve as models for many more human diseases.
Would-be rat cloners had become frustrated because unfertilized rat eggs typically begin dividing within an hour of their removal from a female's oviduct. That didn't allow enough time to pull off the pivotal initial step of cloning: removing an egg's DNA and transferring in DNA from the cell of another animal.
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