Babies made without mothers could come sooner than we think, leading biologists claim.

Late last year, a team at the University of Bath discovered that sperm and skin cells - or any other kind of non-egg cell - might be all you need for conception.

At the time, they said the scenario of men conceiving with men was 'speculative and fanciful'.

But in a new report published today, the top embryologists at Harvard and Brown Universities urge nations to begin contemplating the legal minefield that would surround mother-less babies.

'With science and medicine hurtling forward at breakneck speed, the rapid transformation of reproductive and regenerative medicine may surprise us,' they write.

The injection of sperm into a parthenogenote mouse embryo, pictured. If injecting sperm into a mammalian parthenogenote can produce offspring, theoretically at least it should be possible to achieve the same result using mitotic cells not derived from eggs

HOW COULD THIS BE USED? Gay men, for instance, could have babies with each other, and a man could even fertilize his own cells to produce offspring containing a mixture of genes inherited from him and his parents. More realistically, the technique could allow women whose fertility has been wiped out by cancer drugs or radiotherapy to have their own children. While eggs can be frozen before cancer therapy and later fertilized in an IVF clinic, currently nothing can be done once they have been lost. Conception using sperm and somatic cells would also aid the preservation of endangered species, since it avoids the need to recover eggs. Advertisement

'Before the inevitable, society will be well advised to strike and maintain a vigorous public conversation on the ethical challenges of IVG [in vitro gametogenesis].'

Eggs can be tricked into developing into an embryo without fertilization, but the embryos, called parthenogenotes, die after a few days.

Scientists at Bath have developed a method of injecting mouse parthenogenotes with sperm so they can go on in many cases to become healthy pups.

Working with mice, the team produced healthy offspring while bypassing the normal process of fertilising an egg cell with sperm.

Although the embryos in the experiment started out as egg cells, the experiment raises the prospect that one day they could do the same with adult cells.

Writing in Science Translational Medicine, Dr. Eli Adashi of Brown University, I. Glenn Cohen, professor at Harvard Law School, and Dr. George Daley, dean of Harvard Medical School, warn this is something that they have contemplated for a while.

'These things may happen, and it may just be a question of time,' said Dr Adashi, who has been tracking the development of IVG, mostly in Japan and the United Kingdom, since 2005.

For years, scientists at their institutions have been looking at the idea of IVG, which holds the promise of radically advancing fertility and the ability to intervene against disease at the pre- or post-embryonic stage.

But it also could lead to ethical nightmares - if people become empowered to create and choose among scores of embryos in the pursuit of ideal children, for example.

'There's something troubling about an inexhaustible supply of gametes that can be fertilized into an inexhaustible supply of embryos,' said Dr Adashi, professor of medical science and former dean of medicine and biological sciences at Brown University.

Producing sperm or eggs without the need for functioning reproductive organs could help patients for whom reproductive function has been lost.

This could be because of chemotherapy or a disease, the authors wrote.

HOW SKIN CELL BABIES ARE MADE The discovery that embryos could be made with skin cells was made at the University of Bath. For the experiment, the scientists started off by creating 'parthenogenote' mouse embryos. These are all-female embryos made without sperm by tricking an egg into developing as if it has been fertilised. Mammalian embryos produced this way usually die after a few days because they lack the right programming. But Dr Perry's team of researchers found injecting the parthenogenotes with sperm transformed them into normal embryos that went on to produce healthy offspring. The outcome, reported in the journal Nature Communications, is hugely significant because parthenogenotes share much in common with ordinary cells such as skin cells. In the study, 30 mouse pups were born with a success rate of 24 per cent. This compares with a 1 per cent to 2 per cent success rate for offspring created by the Dolly the Sheep method of cloning by transferring DNA to donated eggs. Some of the mice went on to have offspring themselves, and a number had offspring that went on to have their own pups. Fertility is generally seen as a sign of fitness and good health. Advertisement

IVG could also revolutionize in vitro fertilization because it could vastly expand the supply of eggs.

Currently they must be drug-induced and then surgically harvested in very small quantities and at great expense.

Healthy men have no trouble producing sperm by the millions.

But the possibility of an abundant and cheap supply of eggs - made from sloughed skin or a cheek swab - is the most concerning, Dr Adashi said.

Future physicians could root out some inherited diseases even before fertilization occurs, the authors wrote.

They could also more easily study disease and development at the molecular and cellular level.

Two-cell embryos pictured, produced during an experiment by the University of Bath which opened a window to a sci-fi future in which babies are conceived from skin cells. For the experiment, the scientists started off by creating 'parthenogenote' mouse embryos

Furthermore, people could also generate personalized embryonic stem cell lines for future medical needs, using existing technology to transfer a nucleus from one of their mature body cells into an enucleated egg cell.

But ethical minefields abound - particularly around the idea of 'designer babies'.

Many people are adamantly opposed to creating embryos for research or therapeutic use and in an IVG-enabled scenario in which that's done easily in a lab, the ethical questions are magnified.

Current U.S. law prohibits public funding for the creation of embryos for research.

Clinical uses of IVG will certainly undergo tough regulatory scrutiny in most any country.

'IVG may raise the specter of 'embryo farming' on a scale currently unimagined, which might exacerbate concerns about the devaluation of human life,' Cohen, Daley and Adashi wrote.

WHY IS THIS SIGNIFICANT? If living offspring can be conceived from a parthenogenote mouse embryo, it should also be possible to create babies from skin cells - or cells from other tissue - using the same technique. The work challenges the dogma held for almost 200 years that only eggs fertilised with sperm cells can produce living mammalian offspring. If in future babies can be conceived by injecting ordinary non-egg cells, such as skin cells, with sperm, the ramifications will be huge and highly controversial. But the research is at a very early stage. Difficult obstacles would have to be overcome before the parthenogenotes used by the scientists can be replaced with ordinary cells. The scientists stress that some of the more far-fetched scenarios are 'speculative and fanciful' - but they do not rule them out. They do plan to move on to ordinary cells. Advertisement

'IVG could, depending on its ultimate financial cost, greatly increase the number of embryos from which to select, thus exacerbating concerns about parents selecting for their 'ideal' future child.'

In the most speculative scenario, Adashi says IVG might enable single-parent babies, in which one person produces both sperm and egg, leaving no need for a second parent.

It's not yet clear, however, that a person can produce the other gender's gametes via IVG.

It could be that producing a baby with just one parent's genes - the ultimate in inbreeding - would be to risk the baby's health.

Finally, it's even conceivable that people could be made parents without their knowledge or consent.

'Should the law criminalize such an action?' Cohen, Daley and Adashi asked.