Britain is granting doctors permission to screen test-tube embryos for a gene that makes colon cancer more likely.

Britain's Human Fertilization and Embryology Authority authorized a medical laboratory at University College Hospital in London to screen embryos,  fertilized human eggs that have begun to develop and multiply, for the gene before they are implanted in their mothers' wombs.

Parents who carry the familial adenomatous popyposis gene have a 50 percent chance of passing it on to their children, who would likely develop colon cancer between the ages of 20 and 40.

Doctors say they can detect the cancer gene when a human embryo has grown to about eight cells in size - extremely tiny, but still large enough so that one cell could be removed for testing without harming the embryo.

With the screening procedure, couples could choose to implant only embryos free of the gene.

The ruling opens the way for such genetic testing to be used against many other diseases that might take years or decades to develop. 

Opponents say the tests deny life to embryos rejected by the screening process.

Some information for this report provided by AFP.