Science: Genes on Main Street

Like the electron, the gene has eluded the eye of Science while manifesting itself by its works. “Gene” is the name by which geneticists agreed to call the mysterious heredity-transmitting agents strung along the length of the chromosome. As minute streaks in body cells, the chromosomes were visible under the microscope; their component parts were not. Last week a long step toward visual study of genes seemed to have been taken by Dr. Calvin Blackman Bridges of the Carnegie Institution, working at the Station for Experimental Evolution in Cold Spring Harbor, N. Y.

For many a year Dr. Bridges worked under Thomas Hunt Morgan of Caltech. It was Dr. Morgan who demonstrated the localization of transmitting units on the chromosomes, “linkage groups” (tendency of certain characteristics to be transmitted in groups), and “crossing over” (interchange of genes between male and female chromosomes). For his laboratory animal Dr. Morgan used hardy, quick-breeding Drosophila melanogaster, commonly known as the fruit fly. His reward was the Nobel Prize (TIME, Oct. 30).

Few years ago Heitz of Germany showed that the chromosomes in the fruit fly’s salivary glands were greatly enlarged—70 times bigger than the germ-plasm chromosomes. Last year Dr. Theophilus Shickel Painter of University of Texas found cross bands on the giant chromosomes which he thought might have something to do with gene locality. Then affable, bushy-haired Dr. Bridges refined his photomicrographic technique to such a point that the chromosomes appeared as twisted strings of flat, irregular beads, and the cross bands were seen to be mosaics of infinitesimal cylinder ends. Dr. Bridges did not identify either bands or cylinders with the genes themselves, but by last week three known and one unknown gene had been traced to a set of four bands, and the others, Dr. Bridges predicted, would be “as easily located as the houses on Main Street.”