●Silent clones speak up. Reik, W. & Dean, W. Nature 22 May (2003). As development progresses, transcriptional silencing of genes increases. The authors of this News and Views article use recent experimental data to argue that mammalian cloning is inefficient, probably because genes that are needed for early development are not reactivated.

●Cancer genetics and drug discovery in the zebrafish. Stern, H. M. & Zon, L. I. Nature Reviews Cancer July (2003) The zebrafish has been an excellent model organism for developmental biologists. The authors of this Perspective argue that, in the future, zebrafish studies are likely to make important contributions to cancer genetics and drug discovery.

●The advantages of recombination. Carvalho, A. B. Nature Genetics June (2003) Experiments with the fruitfly Drosophila miranda have shown that recombination is needed for the incorporation of beneficial mutations as well as the elimination of deleterious mutations. The authors of this News and Views piece discuss the wider consequences of this work.

●Genetic code expansion. Giegé, R. Nature Structural Biology June (2003) The degeneracy of the genetic code means that it should be possible to artificially expand it. However, this would require engineering tRNAs and synthetases with new properties. This News and Views article discusses the technical issues involved.

●Calcium signalling during embryonic development. Webb, S. E. & Miller, A. L. Nature Reviews Molecular Cell Biology July (2003) The authors of this Review discuss the functional significance of calcium signalling in embryonic development.

●Occurrence of leukaemia following gene therapy of X-linked SCID. Kohn, D. B., Sadelain, M. & Glorioso, J. C. Nature Reviews Cancer July (2003) The successful gene therapy of children with X-linked severe combined immune deficiency was marred by the development of leukaemia in two patients. The authors of this Review assess how the therapeutic benefits of gene therapy can be achieved while minimizing risk to the patient.

●Molecular detection of pheromone signals in mammals: from genes to behaviour. Dulac, C. & Torello, A.T. Nature Reviews Neuroscience July (2003)

●Nature Encyclopedia of the Human Genome. This new reference resource from the Nature Publishing Group contains more than 1,000 articles about the science of genome research and its ethical, philosophical and commercial implications.