1950s: Scientists begin work on cloning frogs.

1956: The first successful intravenous infusion of bone marrow in patients receiving radiation and chemotherapy is carried out at Mary Imogene Bassett Hospital, New York state.

1978: Louise Brown is the first IVF baby born after fertilisation of a human egg outside the womb by Cambridge scientists.

1981: Mouse embyronic stem cells are cultivated at the universities of Cambridge and California.

1988: The first umbilical cord blood transplant takes place.

1990: The Human Fertilisation and Embryology Act is passed.

1995: Researchers at the University of Wisconsin isolate the first embryonic stem cells in primates.

1996: Birth of Dolly the sheep, the first mammal “cloned” through cell nuclear replacement technique.

1998: Researchers in Wisconsin create human embryonic stem cells.

2003: The UK’s first human embryonic stem cell line is generated at King’s College London. In China Hui Zhen Sheng fuses human cells with rabbit eggs to create a new source of embryonic stem cells.

2005: The Government sets up the UK Stem Cell Initiative to draw up a vision for stem-cell research over the next decade.

2006: Researchers in Edinburgh make an advance in maintaining embryonic stem cells in a state in which they can turn into almost any cell type.

2007: A new stem cell found in rats and mice is deemed to be similar to human embryonic stem cells by scientists working independently at Oxford and Cambridge universities.

June 2007: The International Stem Cell Forum characterises 59 human embryonic stem-cell lines.

November 2007: Bill allowing the creation of hybrid embryos announced in Queen’s Speech.

May 12, 2008: The HFE Bill is due to receive a second reading in the House of Commons