It's fortunate that nature keeps reusing the same building blocks while constructing organisms as different as yeast cells, worms, flies, mice, and humans. This frugality makes it possible for us to learn what our own genes do (which is still largely a mystery) by analyzing similar genes in tiny, rapidly reproducing "model organisms"—organisms that scientists can manipulate with ease in the lab and have come to know very well.

Our genes are actually so similar to those of yeast, fruit flies, nematode worms, and mice that in some cases human genes can be substituted for theirs and work just as well. However, even a slight similarity between a human gene and one from a model organism is generally enough to give scientists valuable hints about the human gene's role in health and disease.

Even though researchers are rightly proud of their tremendous achievement in sequencing the entire human genome (that is, deciphering the sequence of all 3 billion base pairs in human DNA), they would be unable to make much use of this treasure if they did not have access to the information provided by model organisms. This information is also vital to scientists' hopes of developing a new generation of tailor-made treatments for diseases ranging from Alzheimer to many types of cancer.

Key findings about human genes have come from studying the humble, blob-like cells of baker's or brewer's yeast, which one researcher calls, shockingly, our relatives. In 1996, yeast became the first eukaryote (an organism whose genetic material is enclosed in a cell nucleus) to have its entire genome sequenced. Ever since, it has remained at the forefront of research on genetics. Almost everything we know about the cell-division cycle, for instance, comes from experiments with yeast, and many new methods of analyzing genes were first tried out in yeast.

A good example is the do-it-yourself "microarrayer," a robot designed by HHMI investigator Patrick O. Brown at Stanford University. The robot can analyze all 6,000 genes in a yeast cell simultaneously and compare the activity of different sets of genes under various conditions. Whole-genome analysis of this sort promises a revolution in biology. To make the robot widely available, Brown has posted instructions for building it on the Web. Microarrayers have now spread to many labs around the world, where they are used to study not only yeast but other model organisms and even human cells.

— Maya Pines

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