One of the biggest barriers to public acceptance of transgenic crops has been the presence in those crops of antibiotic marker genes. Previously developed systems to generate marker-free transgenic plants were either unreliable or not applicable to crops propagated by seeds (i.e., most crop plants). On page 157, Zuo et al. develop a chemical-inducible DNA excision system in transgenic Arabidopsis plants. They introduced into the Arabidopsis genome the Cre recombinase gene and the marker gene flanked by loxP recombination sites. They then induced the recombinase gene with β-estradiol to eliminate both itself and the linked marker DNA from the genome. The induction system shows remarkably tight control and high recombination efficiency (see also p. 115).