In Pursuit of the Gene

318 ¨ NOTES TO PAGES 157–160
38. McClung gives a thorough review of the literature on accessory-chromosomelike
structures in C. E. McClung, “The Accessory Chromosome: Sex Determinant?”
Biological Bulletin 3 (1903): 43–84.
39. Clarence McClung, “The Spermatocyte Divisions of the Acrididae,” Kansas University
Quarterly 9 (1900): 95.
40. Walter S. Sutton, “Spermatogonial Divisions in Brachysola Magna,” Kansas University
Quarterly 9 (1900): 135–160.
41. Spermatogonia arise from undifferentiated germ cells. After eight or more
generations of division, spermatogonia give rise to primary spermatocytes, each of which
divides twice to give four spermatids, the immediate precursors of the sperm cells
(also called spermatozoa).
42. The paper was rejected by the Journal of Morphology. More than two years after its
first submission, the paper was published in Biological Bulletin. McClung refers to the
long delay in publication in C. E. McClung, “Notes on the Accessory Chromosome,”
Anatomischer Anzeiger 20 (1901–1902): 220–221.
43. C. E. McClung, “The Accessory Chromosome, Sex-Determinant,” Biological
Bulletin 3 (1902): 74–75.
44. Ibid., 73–74.
45. Sutton first reported that the female lubber had 22 chromosomes, and the
male 23, in 1902. See Walter S. Sutton, “On the Morphology of the Chromosome
Group in Brachystola Magna,” Biological Bulletin 4 (1902): 35.
46. McClung, “Accessory Chromosome,” 82. During the year and a half that had
elapsed since the submission of the original manuscript, McClung had also witnessed
the splitting of the accessory chromosome into two chromatids, which further
strengthened the view that it was present in exactly half the spermatozoa.
47. Walter Stanborough Sutton, 61–62.
48. There were two opinions concerning the mechanism of the reduction in
number of the chromosomes. Sutton assumed that the homologous chromosomes
were joined end to end, which was known as telosynapsis, and that each pair was
then cut in half in the next division. The other view was that the homologous
chromosomes lay side by side, which was known as parasynthesis, and that the
pairs were split lengthwise. It wasn’t until 1912 that Wilson, who was by then the
leading exponent of the chromosome theory, weighed in favor of the side-by-side
conjugation (Wilson, “Chromosomes VIII,” Journal of Experimental Zoology 13 [1912]:
348–349).
49. Sutton mistakenly believed that the reduction in chromosome number took
place in the second meiotic division. Confusion over this point persisted in the lit-