When introducing foreign genes into plants, scientists must also introduce a resistance gene to herbicide or antibiotics–this allows the cells with the incorporated transgenes to be regenerated on selectable media. However, while it has not ben demonstrated that marker genes can “escape” to weedy relatives or gut bacteria, their safety has nonetheless become a flash point in the debate over safety of GM foods. Since marker genes are only needed during the plant transformation process, it should be possible to remove marker genes from crops after the transgenic material has been selected, which would improve the public acceptance of genetically engineered crops. On page 442, Meyer and colleagues describe a vector that mediates deletion of marker genes from transgenic tobacco. They placed the marker gene, which confers resistance to kanamycin, between bacteriophage lambda sequences called Attachment P regions, which mediate intrachromosomal recombination. They also included a gene called tms2, which inhibits growth in the presence of certain hormones, and therefore can be used to select transformants in which the marker gene was deleted through intrachromosomal recombination.