Rat joins list of cloned animals

Cloning will aid in the development of genetically modified rat models of greater predictability and quality.
Scientific results obtained from these models will contribute to the development of innovative therapeutics for major pathologies such as cardiovascular diseases, cancers, obesity, diabetes and neurological disorders.

Rats and mice used in labs are inbred or genetically engineered to have certain traits -- such as a weak immune system, or a tendency to cancer.

So-called knock-out mice and rats lack certain, specific genes and are useful for finding out what an unknown gene does.

Cloning such animals will guarantee they are genetically identical for careful experiments. Rats, it turns out, are more difficult to clone than sheep, cattle or even mice.

They evolved to reproduce fast and their eggs begin to activate almost as soon as they leave the ovary. This posed a problem for a technology that requires painstakingly removing an egg cell, taking out its nucleus, and replacing it with the nucleus from a skin or other kind of cell from the animal to be cloned.

Genetic researchers described how they did it. They impregnated two rats with cloned embryos and produced three live pups, one of which died soon after birth. They bred the two remaining pups, which fathered normal offspring, and have since cloned two female rats, as well.