But his cells came from macaques, not humans, and his technique involves destroying the embryo.

ECONOMIST: Human embryonic stem cells

Preimplantation genetic diagnosis (PGD), the technique used to see if an embryo is a match, is legally permitted now if a genetic condition is present in a family.

BBC: Embryology Bill: The key points

In mice, Daley and colleagues have shown that stem cells derived from the nuclear transfer of cells to make embryos -- the technique described in Mitalipov's paper -- were indeed closer to natural embryo stem cells than induced pluripotent stem cells.

CNN: Cloning stem cells: What does it mean?

Even more radical was the invention, in 1978, of in-vitro fertilization, or IVF, the now-common technique in which egg and sperm meet in a laboratory petri dish and create an embryo that is then implanted in the would-be mother's womb.

CNN: Science led to gay families: Law should follow