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worked out and the homogentisic acid isolated and identified many years
before.

Our idea — to reverse the procedure and look for gene mutations that in-
fluence known chemical reactions — was an obvious one. It followed logically
from the concept that, in general, enzymatically catalyzed reactions are gene-
dependent, presumably through genic control of enzyme specificity. Although
we were without doubt influenced in arriving at this approach by the antho-
cyanin investigations, by Lworr’s demonstrations that parasites tend to
become specialized nutritionally through loss of ability to synthesize sub-
stances that they can obtain readily from their hosts (18), and by the specula-
tions of others as to how genes might act, the concepts on which it was based
developed in our minds fairly directly from the eye-color work EpHrussi and
I had started five years earlier.

The idea was simple: Select an organism like a fungus that has simple nutri-
tional requirements. This will mean it can carry out many reactions by which
amino acids and vitamins are made. Induce mutations by radiation or other
mutagenic agents. Allow meiosis to take place so as to produce spores that
are genetically homogeneous. Grow these on a medium supplemented with
an array of vitamins and amino acids. Test them by vegetative transfer to
a medium with no supplement. Those that have lost the ability to grow on
the minimal medium will have lost the ability to synthesize one or more of the
substances present in the supplemented medium. The growth requirements
of the deficient strain would then be readily ascertained by a systematic series
of tests on partially supplemented media.

In addition to the above specifications, we wanted an organism well suited
to genetic studies, preferably one on which the basic genetic work had already
been done.

Neurospora.

As a graduate student at Cornell, I had heard Dr. B. O. DoncE of the

__New York Botanical Garden give a seminar on inheritance in the bread mold

Neurospora. So-called second division segregation of mating types and of
albinism were a puzzle to him. Several of us who had just been reviewing the
evidence for 4-strand crossing over in Drosophila suggested that crossing over
between the centromere and the segregating gene could well explain the result.

DopcE was an enthusiastic supporter of Neurospora as an organism for
genetic work. “It’s even better than Drosophila”, he insisted to Tuomas Hunt
MORGAN, whose laboratory he often visited. He finally persuaded MorcAN