Science: Jumping Genes

Honors to the Corn Lady

She is something of a scientific anachronism, and not because of her 79 years. Unlike most scientists at the famed biology laboratory in the small Long Island, N.Y., town of Cold Spring Harbor, she does not splice, cut or reshuffle the genes of viruses and bacteria. Rather, for the past four decades, Geneticist Barbara McClintock has been carefully breeding and crossbreeding corn, trying to cull from it some kernels of truth about the secrets of genetic diversity, just as the Austrian monk Gregor Mendel did in his famous pea patch more than a century ago. McClintock’s colleagues, caught up in the latest wizardry of genetic engineering, have long marveled at the skill and diligence with which she pursued such classical genetics, but they were sometimes patronizing about her work. After all, it seemed totally out of the mainstream of molecular biology, today’s hottest science.

The judgment was premature. In the twilight of her career, McClintock is suddenly being hailed as a scientific prophet. This year she has received eight awards, the richest and most prestigious just last week: a $60,000-a-year, taxfree, lifetime grant from Chicago’s MacArthur Foundation and the Lasker prize for basic research, worth $15,000 and often a steppingstone to a Nobel Prize.

Few of McClintock’s colleagues believed in her ideas when she first considered them in the 1940s. After majoring in biology at Cornell, and adding a botany Ph.D., she began methodically cultivating maize on a little plot near an inlet of Long Island Sound. McClintock, funded by the Carnegie Institution of Washington, kept careful watch over the kaleidoscopic changes of color in the leaves and kernels of corn from one generation to the next. The changes were produced by underlying modifications in genetic structure. At the time, though, no one understood how DNA was put together or how it worked. Indeed, only a few researchers were convinced it really was the molecule that carried heredity’s message across the generations. The only signs of genetic change within the cell itself that McClintock could look for were such things as breaks or alterations in the cell’s chromosomes, rodlike bodies that even then were known to be the residence of the elusive genes.

On some kernels, McClintock began finding curious, quirky patterns of pigmentation. A less imaginative scientist might have dismissed them as natural variations occurring at random. But through painstaking record keeping and careful analysis, McClintock discerned a method in nature’s seeming madness. The pigment genes, those causing the splotch es of color on the kernels, were somehow being switched off or on in a particular generation. Still more remarkable, the same “switches” often seemed to crop up a generation later at different places along the same chromosome or even on a totally different chromosome. Indeed, these mysterious “controlling elements,” as McClintock called them, seemed to be available almost any place in the genetic machinery where they might be needed to turn genes on or off. Such moments come in particular during the early stages of a plant or animal’s development, when one type of cell miraculously produces entirely different cells to form all the variegated tissue of the whole organism.

When McClintock formally unveiled her research in 1951, the prevailing wisdom was that genetic structure was stable and immutable. “They called me crazy, absolutely mad at times,” she recalls. It was not until about ten years ago, when scientists were able to use the powerful new tools of genetic engineering, that they found the first indications that McClintock’s transposable elements—actually bits of DNA—do move about. Such jumping genes, in fact, could turn out to provide significant insights into a number of major biological mysteries. These include not only the question of how whole organisms develop from single cells, but how entirely new species may arise—and even why some cells occasionally go berserk, as in the case of cancerous cells. Says Nobel Laureate James Watson, co-discoverer of DNA’s architecture: “She is a very remarkable person, fiercely independent, beholden to no one. Her work is of fundamental importance.”