The big-tomato gene

Quantitative trait loci (QTLs) are genes whose variation controls continuous characteristics such as height and weight. Multiple QTLs for a single trait have made for complicated genetics and slow progress in moving from correlation to work with single genes. But in the July 7 Science Frary et al. isolate fw2.2, a gene whose small-fruit version can reduce the size of tomato fruit by 30% (Science 2000, 289:85-88). The gene is expressed at higher levels in the carpels (which ultimately develop into fruit) of small-fruited plants. These carpels have fewer cells, and the predicted structural similarity of the products of fw2.2 and the Ras oncogene suggest that fw2.2 may play a role in cell cycle control.