FISH identification of the autosomal segment of the neo-W chromosome homologous to the Z2 chromosome in S. cynthia subsp. indet. on female pachytene chromosomes of S. c. walkeri (a) and S. cynthia subsp. indet. (b, c). The Cy3-labelled orthologous probe of the B. mori Topo II gene (red signals, arrowheads) hybridized to an autosomal bivalent but not to the neo-Wneo-Z bivalent in a female pachytene complement of S. c. walkeri (a), whereas in S. cynthia subsp. indet., the probe mapped to the Z2 chromosome and the neo-W chromosome of the neo-WZ1Z2 trivalent (b). The Cy3-labelled orthologous probe of the B. mori RpL18 gene (red signal, arrowhead) also hybridized to the Z2 chromosome and the neo-W chromosome of the neo-WZ1Z2 trivalent in S. cynthia subsp. indet. (c). GISH with Green-labelled female genomic probe (green signals) identified the original W-heterochromatin parts of the neo-W chromosome in S. c. walkeri (a) and S. cynthia subsp. indet. (b, c). Chromosomes were counterstained with DAPI (light blue). Bar represents 10 μm.