When the male of marker strain (pe/pe, p/p) was crossed with spontaneous mutant, mosaic females having translucent and normal skin characters that were found in hybrid race (Kinsyu × Showa) raised on silkworm farms, unexpected segregations were observed.
First one was the appearance of white eggs. Because this is considered normal egg (+pe/+pe) color for the hybrid race (Kinsyu × Showa), the F1 was considered to be completely normal (+pe/pe), but white eggs were about 25% segregated. This was estimated not due to mutation of the pe gene body, but rather to breakage in the vicinity of +pe . Furthermore, it became clear that the fragment chromosome 5, that the +pe was on, was missing in the cell division. However, there was no relation between egg color and sex.
Next, when the translucence of each character of larvae was examined, absolutely no translucent silkworms appeared. On the other hand, when the larval marking of these individuals was examined. 1:1 segregation between normal marked silkworms and plain silkworms had been expected, but it was actually a segregation of about 2:1. Furthermore, although it had been thought there was no relation between larval marking and sex, there was only females in normal marked silk-worms, but almost none in males. In contrast, it was the exact opposite in plain silkworms, where there was much males in plain silkworms, and almost none in females. The cause is thought to have been the distortion of segregation originating in the mutual translocation between the Z chromosome and chromosome 2. In addition, when the breakpoint of the Z chromosome was examined, it appeared that there was breakage between the +od gene and the +ℓ2 gene.