Legislation currently making its way through the British parliament aims to dramatically widen the acceptable scope of assisted reproduction and embryo research in the UK. One of the bill’s provisions permits the creation of in vitro siblings with matching tissues that can be harvested in case the original child needs an organ or bone marrow transplant later in life.

Among the bill’s other notable provisions:

• A reduction of the 24 week window for legal abortions
• A ban on sex selection of offspring for non-medical reasons
• Permission to create “cybrids” — human-animal hybrid embryos for medical research

Creating human-animal hybrid cells

The third provision — creating human-animal embryos — has drawn the most controversy. The process involves inserting human DNA into animal eggs. Before a human cell nucleus is inserted into the animal egg, the animal nucleus is removed. The process rids the cell of most — but not all — animal DNA. And therein lies the controversy: mitochondria in the animal egg’s cytoplasm — the fluid in which mitochondria float — still contain tiny amounts of animal DNA.

Over at The Wild Side New York Times blogger Olivia Judson breaks down the potential problems:

In and of itself, the mitochondrial genome is tiny. Where the main human genome is 3 billion base pairs of DNA long, the mitochondrial genome is a mere 16,500. But that doesn’t mean it doesn’t matter: mitochondria play several crucial roles in the cell, and faulty mitochondria are linked to a large number of human diseases.

Inserting a human cell into an animal egg does, therefore, create a kind of genetic hybrid, for most of the mitochondrial DNA will be of animal origin. (A little will be human, for the skin cell will have brought some with it. Hence the term “cybrid” — for cytoplasmic hybrid.) At least some interspecies clones have run into problems because of a failure of the DNA in the nucleus to communicate correctly with the DNA in the mitochondria.

Benefits of cybrids

Still, proponents of cybrid technology argue that the potential benefits outweigh the risks. If the procedure works, scientists will have an effective way of increasing the supply of human stem cells — cells created immediately after an egg is fertilized that possess the potential to become any type of cell in the body. And that could lead to treatments for all sorts of genetic diseases, like Parkinson’s and Alzheimer’s.

Objections to cybrids

Critics of the process object for a number of reasons. Some are worried that the procedure won’t work, while others worry that mixing human DNA with unfamiliar animal DNA may unleash dormant retroviruses asleep in the human genome. Others object on religious grounds. They contend that the mixing of human and animal DNA compromises the sanctity of life.

14-day window of opportunity

To those who object on moral grounds, Ms. Judson points out that the parliamentary bill will require cybrids to be destroyed after 14 days. That way, the cybrids won’t be able to divide into different cell types. Instead, they will remain “tiny clumps of cells [that] can potentially lead to treatments that improve peoples’ lives.”

What do you think?

Does the prospect of human-animal hybrid cells — even if they are just “tiny clumps” — creep you out? Do you harbor deep reservations about the spiritual implications of this procedure? Or are you excited by the potential medical breakthroughs that may result? Share your opinion in the comments field below. And while you’re at it, take a moment to ponder the question: Would you clone your dog?