In Pursuit of the Gene

CHAPTER 12
X-Rays
¨ WITH THE RESOLUTION of the beaded and truncate cases, the
last serious doubts about the universality of Mendelism and the chromosome
theory were extinguished. However, genetics, as William Bateson had
defined the word in 1905, was the study of two central topics, heredity and
variation, and while the problem of inheritance was more or less solved, the
study of variation had barely progressed at all in fifty years. Furthermore,
Muller had succeeded in discrediting De Vries’s mutation theory, which
had been the only promising lead. But having cleared the field, Muller was
now free to make a new mutation theory.
As he wrote to Julian Huxley, almost nothing was known about the
topic: “We simply know that mutation occurs, and occurs ‘rarely’, whatever
that means, though in fact on its rate and mode of incidence depend
evolution.” 1 In fact, the rate of appearance of new mutations was so low—
the best estimate was that 1 in 50,000 flies contained a new mutation—that
it was difficult to conceive of how one might study the problem at all.