UK starts study on using human DNA in animals. Human ear grown on mouse's back. Plans to create human embryos using empty cow and rabbit eggs. Experts have been swapping human and animal DNA for years. There are two main types of experiments: altering an animal's genes by adding human DNA and replacing a specific animal sequence with its human counterpart. Scientists also have tried to grow human organs in animals that could one day be transplanted back into humans ? like a mouse onto whose back scientists grew a human ear
