Human/animal hybrids (link). It's not a new idea, but it raises some interesting issues in terms of the protection of human life, and the definition of "human." Does the substitution/insertion of a short "alien" genetic sequence render a human embryo non-human? Does the substitution/insertion of a short human genetic sequence render a non-human embryo human?
Obviously, the scientists are not going to treat the hybrids as though they are people, and yet are interested in them precisely because of their genetic derivation from people.