In Pursuit of the Gene

158 ¨ CELL BIOLOGY
Although he made a truly inspired deduction, McClung then went
wrong. Assuming that the function of the extra chromosomes was to
“carry the transformation beyond the production of ova to sperm,” he was
convinced that the X chromosome contained factors that facilitated this
transformation and therefore would be found only in males. 44 More than
two years after its initial submission, McClung’s tour de force “The Accessory
Chromosome: Sex Determinant?” was finally published in the Biological
Bulletin in 1903. In the period between the first submission of the paper and
the publication of the final version, Sutton had become convinced that the
female lubber grasshopper had 22 chromosomes while the male had 23. 45
Such a finding, had it been true, would have greatly supported the theory
that the accessory chromosome was male-determining, and it was undoubtedly
partly in response to Sutton’s finding that McClung added an
addendum to his original paper. “Regarding the theory of its function advanced
in this paper,” he now added, “I can say only that it has, if anything,
been strengthened by later researches.” 46 But it turned out that Sutton had
been wrong, and he had missed one chromosome pair in female ovicular
cells, which were far less plentiful and more difficult to work with than
male testicular cells. Later analysis would show that females had 24 chromosomes
and males had 23, which suggested that males had one copy of
the accessory and females had two. Contrary to McClung’s speculations, it
appeared that maleness was determined by the lack of a second copy of the
X chromosome.
In the meantime, it had become clear to McClung that Sutton could
not realize his full scientific potential in Kansas. Although McClung was
deeply attached to his star student, McClung urged him to pursue a Ph.D.
degree with Edmund Wilson at Columbia and helped him secure a fellowship.
McClung recalled helping Sutton pack on his last night in Russell and
then falling asleep on a lab bench. “In the morning with a heavy heart I
said good-bye,” he later wrote describing their final night together, “and
saw him pass from under my halting and immature guidance into that of
the best men the country afforded—and the pleasure was near as great at
his good fortune as if it had been my own.” 47
With Wilson’s expert guidance, Sutton now continued his study of the
male grasshopper chromosomes. Having already noted that there were