A new study that tests how human DNA is used in animal experiments gets underway Tuesday in the United Kingdom.
British scientists say they want to determine where the line should be drawn. They say that current regulations aren't clear as to how much DNA can be put into an animal.
This comes after a controversy that occurred two years ago when scientists announced plans to create human embryos using empty cow and rabbit eggs.
One stem cell expert says it's worth studying if a cure could be found for any horrible disease. However, one watchdog group says such experiments aren't warranted.