A US advisory board has debated a controversial new technique that would use DNA from three people to produce embryos free of a particular type of hereditary disease. The panel which provides independent advice to the US Food and Drug Administration yesterday weighed whether a procedure that replaces part of a human egg cell with that of another is safe for clinical trials. The procedure has thus far been tested only on monkey embryos. Proponents of the technique called 'three-parent in vitro fertilization' say the measure has huge medical potential while detractors say it could lead to custom-made 'designer babies.'