In Pursuit of the Gene

92 ¨ MENDEL
brids, following the injunction of his teacher Unger to “reduce the phenomena
of life to known physical and chemical laws.” 24 He’d already been
crossing grey and white mice in his rooms, observing the coat color of the
offspring, and at the same time he’d been producing new color varieties
from crosses of different flowering plants. While he was not free to discuss
the results of his rodent-breeding experiments, which would have been
viewed as immoral by the church authorities, he was deeply impressed by
“the remarkable regularity with which the same hybrid forms continually
recurred when the fertilization took place between like species,” as he put it
in his later account.
By 1854 Mendel had settled on the common garden pea, Pisum, as the
most suitable object for his studies of the behavior of hybrids. Pisum offered
great advantages that had been recognized by several other investigators,
including Darwin. Not only did crosses of Pisum varieties yield fertile hybrids,
but the fact that the sexual parts of each flower were enclosed in a
capsule (known as the keel) made Pisum a wonderfully convenient plant in
which to make artificial crosses. Ordinarily the pollen-bearing anthers burst
inside the closed capsule, but it was possible to cut open the keel of stillimmature
flower buds, cut out the anthers, and immediately dust the female
parts with foreign pollen.
In the legendary paper describing the account of his research, Mendel
created the impression that the conclusions of one experiment led him to
the design of the next, but in this he was likely bowing to the conventional
view that the only way to scientific truth was through experiment. As was
first suggested by R. A. Fisher, Mendel’s experiments were surely designed
to prove a point and not “for his own enlightenment.” 25 Unlike Gaertner
and many of the other hybridists, who viewed species as indissoluble entities,
and hybrids between species as a test of supremacy of one type over another,
Mendel appeared to assume that a species was a mosaic of factors
that were randomly shuffled in the process of sexual reproduction.
In the simplest case, Mendel considered a hybrid formed from parents
that differed in only one major factor, which he denoted by capital A or
lowercase a. In the process of reproduction, egg and pollen cells were produced
containing one or the other of the factors with equal probability, and
it was strictly a matter of chance which kind of pollen joined with each