Researchers think they have found the reason why many clanes die either as fetuses or newborns die either as fetuses or newborns. In cloning, the DNA of an adult animal is inserted into a donor egg that has been cleared of its original DNA. To make the cell develop, genes that were turned off in the adult animal being cloned must be turned on again, to make the animal inside the egg be an identical inidvidual. The embryo in females receives two x Chromosomes. Each one contains several hundred genes. In natural reproduction, the genes on the two X chromosomes are active in female embryos. Scientists found that the genes had been imcompletely reprogrammed in 5 dead cow clones. Cloning is being eyed for dairy and beef cattle to reproduce the genetic traits that make those animals commercially valuable.

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