In cutting-edge experiments, scientists have injected human brain cells into monkey fetuses to study the effects. Critics warn that these experiments may accidently produce monkeys with brains more human than animal, posing a new set of ethical issues.

After seven years of debate, the U.S. Patent and Trademark Office has denied a scientist a patent for a genetic chimera that is part human and part animal. The ruling was a victory for the scientist who was trying to create legal precedent against the creation of human-animal chimeras but it also raises serious questions about using the Patent office to govern emerging genetic technologies.

Researchers are debating the ethics of creating chimeras -- creatures that are part animal and part human.

North American scientists are considering whether to implant stem cells from
a human embryo into a mouse embryo ? a controversial experiment that could
result in a mouse-human mix reminiscent of mythological monsters.