With this knowledge, Morgan and his students began the first chromosomal map of the fruit fly Drosophila.

They monitor when certain genes are activated in the course of maturing so they can develop their own chromosomal map."

Even a preliminary chromosomal map that generally locates some of its gene functions, when combined with what is known from traditional breeding, would be an enormous boost for alfalfa research, Dr. Long said.

And his painful familiarity with the possibilities of sheer accident - his achondroplasia is "the product of pure, malign chance" - evokes the image of a capricious God randomly sticking pins in our chromosomal map.

Now in a slick feat of molecular maneuvering, a team of researchers has reorganized huge portions of one yeast species' chromosomes, rendering its chromosomal map identical to that of a closely related species, just as it was once, in the distant past.

But botanists have recently been able to follow three or four plant genes simultaneously through the generations, so long as they have a good chromosomal map of the species under study; in the case of dogs, Dr. Rine estimates such a blueprint will take three to five years more.