Q What are interspecies embryos?

AThey are embryos that are partly human and partly animal, and there are three broad types. Cytoplasmic hybrids or “cybrids” are made by inserting human DNA into an empty animal egg (usually a cow’s), and are genetically 99.9 per cent human. Chimeras are mixtures of human and animal cells. True hybrids are made by fertilising an animal egg with human sperm, or vice versa, and contain 50 per cent of the DNA of each.

Q What has the Human Fertilisation and Embryology Autho (HFEA) approved?

A It has agreed in principle to the creation of cytoplasmic hybrids. No decision has yet been taken on the other two sorts of interspecies embryo, in part because no British scientists have yet applied for permission to make them.

Q Why do scientists want to make cybrids?

A They are potentially valuable tools for medical research. The idea is to create cell models of diseases with a genetic element, such as diabetes, Parkinson’s and motor neuron disease.

Q How would this work?

A The nucleus of an adult cell is removed from a patient with, say, diabetes, and placed into an empty cow egg. The resulting embryo is virtually a clone of the patient, containing 99.9 per cent of his or her DNA. This is then split into embryonic stem cells, which can be used to study how the disease develops, and to test new treatments.

Q Why use animal eggs?

A Ideally, human eggs would be used, but these are in very short supply. For the creation of laboratory models, animal eggs are almost as good.

Q Will cybrids be used for stem cell treatments?

A No. The small amount of animal DNA they contain means that there would be a risk of introducing new diseases, so this is very unlikely in the medium term.

Q What are the objections to this research?

A Critics argue that cybrids blur the species barrier and are thus an affront to the sanctity of human life. Most opponents, however, tend to be opposed to all research with human embryos, often for religious reasons. Some scientists also question whether cybrid stem cells will be valid models of human disease, but mainstream research groups, such as the Royal Society and the Medical Research Council, think that they are worth trying.

Q What does the public think?

A An HFEA consultation found that while the work sometimes elicits instinctive opposition because of the “yuck factor”, most people accept it once the rationale is explained. An opinion poll found 61 per cent were in favour if the research might improve medical understanding.

Q What is the legal situation?

A The law as it stands does not cover cybrids explicity, but the HFEA and most legal experts think it has the authority to regulate. A court challenge, though, is likely. The Human Tissue and Embryos Bill, to be presented in the Queen’s Speech, will make it clear that cybrids can be licensed by the HFEA. The Government proposed to ban the work originally, but backed down after protests from scientists.

Q What happens next?

A Within the next three months, the HFEA will rule on applications to make cybrids from two teams, based at King’s College London and the University of Newcastle-upon-Tyne. Both are expected to be approved, clearing the research to begin, subject to any legal challenge. A third application is expected from Ian Wilmut of Edinburgh University and Chris Shaw of King’s, who want to use cybrids to research motor neuron disease.

Q What about chimeras and true hybrids?

A No British research team is presently proposing to make these, and what happens in the medium term will depend mainly on decisions by the Government. At present, the Human Tissue and Embryos Bill will ban true hybrids but allow chimeras, but the hybrid ban was criticised as excessive in July by a scrutiny committee of MPs and peers. Ministers have yet to respond.

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