Fig. 1.

Thin gray bands in some regions of the fourth chromosome. a Illustration drawn by C. Bridges (Morgan et al. 1934). The drawing is practically the same as in the work by Bridges (1935b). b Drawing of C. Bridges (1935a). c–e Light microscopy of the fourth polytene chromosome. Arrowheads and red lines indicate faint gray bands 102C8, 102D8, 102E3, and 102F3