A mouse that can speak? A monkey with Down's Syndrome? Dogs with human hands or feet? British scientists want to know if such experiments are acceptable, or if they go too far in the name of medical research.
The Academy of Medical Sciences has launched a study to look at the use of animals containing human material in scientific research.
Using human material in animals is not new. Scientists have already created rhesus macaque monkeys that have a human form of the Huntingdon's gene so they can investigate how the disease develops; and mice with livers made from human cells are being used to study the effects of new drugs.
But scientists say the technology to put ever greater amounts of human genetic material into animals is spreading quickly around the world -- raising the possibility that some scientists in some places may want to push boundaries.
Religious groups are among those that are uneasy about the trend. One Catholic cardinal, Keith O'Brien of Edinburgh, has branded such work "Frankenstein science."