Science: The Secret of Life

(5 of 9)

Taking a leave from Caltech, Beadle went to Paris to work with Ephrussi. Their first joint experiment was the delicate feat of transplanting an eye from one minuscule fruit-fly larva to another. After many attempts, an eye took hold and lived, and the two young scientists spent a whole day of celebration at a sidewalk café.

This was no mere stunt; it had a purpose—to find out whether the chemicals in one larva's body would affect the color of an eye transplanted from another larva. It did not work, but Beadle remained convinced that the innermost secrets of genetics and of life itself must be approached from the chemical angle.

Skilled Cell. The idea was not original with Beadle. Every biologist marvels at the chemical virtuosity of living cells. Under the eye of the microscope they seem placid things. The slimy protoplasm inside them sometimes streams slowly, but little other action is visible. This quietude is an illusion. The typical cell, which may be only one twenty-five-thousandth of an inch long, is aboil with chemical action. It is building thousands of complex compounds and tearing other thousands to bits. It selects nutrients that it wants, and in some mysterious way absorbs them selectively through its outer wall. Tiny, mysterious bodies move through its protoplasm, and inside the nucleus reside the powerful chromosomes, which most geneticists believe are like a chemical oligarchy controlling the activities of a chemical nation. If the cell is a fertilized egg, the chromosomes possess all the information needed to build the cell into a bug or a whale or a man.

Beadle believed that the easiest way into the chromosomes' citadel would be by finding mutations with single, simple effects on an organism's chemical behavior. This is the chemical approach that revolutionized genetics. Beadle did not really get to work on it until he went to Stanford in 1937 as a full professor, and he wasted several years more before he concluded that fruit flies (almost sacred animals with geneticists) are not the best subjects for chemical genetics.

In 1940 Beadle teamed up with Dr. Edward L. Tatum, a chemist now of the Rockefeller Institute, and selected a new laboratory victim, the so-called red bread mold (Neurospora crassa), which is really a beautiful coral pink in its natural state, unmolested by geneticists. Neurospora is a geneticist's dream. When properly introduced, it mates and reproduces sexually. It also grows nonsexually, so a truckload of mold with the same heredity can be grown, if desirable, from a single spore. But the best thing about Neurospora is that it asks for so little. It thrives on a medium containing nothing but mineral salts, sugar and a single vitamin, biotin. Everything else that it needs it can make out of these simple foods.

Mutated Mold. The Beadle and Tatum plan for Neurospora was to try to create strains that differ from the normal mold in simple, chemical ways. Their method was simple, too. They irradiated mold with X rays to induce mutations. Then they gathered spores formed by sexual reproduction and laid them out on a sheet of agar jelly containing the minimum nutrients that natural wild mold requires. Some of the spores sprouted and grew normally, showing that they had not been mutated in any obvious way. Some were dead, perhaps mutated too much.