Flies don't get kidney disease, and worms don't get heart disease, yet many of the human genes that are faulty in these and other human disorders have parallel genes in model organisms, where they can be studied more easily.

After the fly's genome was sequenced in March 2000, a team of scientists found that 61 percent of the human genes known to be mutated in 289 human diseases have close equivalents in flies. Many of these genes also have parallels in worms and even in yeast.

The extent of similarity between some of the human disease genes and genes that have been sequenced in flies, worms, and yeast is shown below. Genes with the highest degree of sequence similarity are indicated by the filled circle. The next group is two-thirds. And a lower degree of similarity is shown by the one-third filled circle. Empty circles indicate extremely low or no similarity between the genes.

"Some of the human disease genes can be found in yeast—they are very ancient genes," says Gerald Rubin, the report's lead author.* "Some can be found only in worms and flies, and some only in flies. Of course the closest similarity would be with the mouse. Any gene on this list would have a parallel in the mouse."