In Pursuit of the Gene

278 ¨ EPILOGUE
tion of the injected genes into the genome of the receiving bacteria by a
process of crossing over entirely analogous to ordinary crossing over. 1 Furthermore,
he suggested that a similar mechanism explained the observation
that the properties of one bacterial virus could be acquired by another,
the process that he had first called attention to in his 1921 address at the
Toronto meeting of the American Society of Naturalists. Like so many of
his ideas, Muller’s suggestion that these viruses, later called bacteriophage,
could be the model organism of choice in which to study the nature of
genes was prophetic, and by the late 1940s their study had become the driving
force in genetics.
In 1947 the 18-year-old James Watson left the University of Chicago and
enrolled as a graduate student at Indiana University, where he had been
drawn by the presence of Muller. In Muller’s course on advanced genetics
for first-year graduate students, Watson was exposed for the first time to
gene theory, much of which Muller himself had developed. In particular,
Muller had long argued that genes must contain two distinct structural elements.
One feature, which would allow for the copying of a pattern to
take place and whose function would not be influenced by the particular
pattern being copied, would have existed since the dawn of life. The second
feature, somehow embedded in the first, would vary from gene to gene, determining
each gene’s particular function, and at the same time it had to be
capable of mutational change. Figuratively, at least, “and perhaps . . . even
literally,” Muller wrote, the two kinds of arrangements lie in different “dimensions”
from one another. 2
But Muller was even more explicit in his description of the properties
of the molecule, insisting that the embedded feature “must be arranged in
only one or two dimensions.” 3 This was the only way to explain how a
daughter gene copied the pattern of the parent gene. The gene acted as a
template, it was “a modeller, and forms an image, a copy of itself, next to
itself,” he explained. “A duplicate chain is produced next to each original
chain, and no doubt lying in contact with a certain face of the latter.” 4 Furthermore,
he speculated, genes must be made up of smaller units, and he
believed these smaller units would come in relatively few different types (it
would turn out that there are four). It was the unique order in which these