It took a century to go from Mendel's plant-breeding experiments to the genetic code. The Molecular Genetics Explorer can help biology students make the same intellectual journey by connecting changes in an organism's DNA to alterations in its appearance.

The free virtual lab comes from Brian White and Ethan Bolker of the University of Massachusetts, Boston. Students begin by setting up plant crosses and gene mutations to decipher the inheritance of color in fictional flowers. They then move to the protein level, tinkering with amino acid sequences to see how changes alter a protein's shape and the flower color it produces. The final exercises let users determine the consequences of manipulating DNA.

Volume 317, Number 5837, Issue of 27 July 2007