Two centuries of genetics: a view from halftime.

In the first half-century of genetics, 1900 to 1953, the main techniques were breeding experiments and microscopy. Emphasis was on transmission genetics and cytogenetics, and during the half-century these became mature sciences. But the gene remained elusive. In 1953, thanks to Watson and Crick, the nature of the gene was no longer a mystery. In the second half of the century, the techniques became more chemical and computers played an indispensable role. The emphasis was then on gene action and, in the human, on increasingly accurate gene mapping and the soon-to-be-completed DNA sequence. During the first half-century, human genetics was very primitive, but by the end of the century it was comparable to that of the best-studied species. This trend will surely extend to the next century. The humanitarian possibilities of new techniques are enormous, but social judgments about their use and the problems of an increasingly crowded planet temper our optimism.