Figure 4.

Upper panel: FISH with sex chromosome-derived probes in mitotic metaphase complements of parents (a, b) and F₁ (c, d) and F₂ (e-l) offspring of crosses between Samia cynthia walkeri females and Samia cynthia pryeri males. Chromosomes were stained with DAPI (grey). Cy3-labelled probe of the 32B23 fosmid clone (red signals) mapped to chromosome 13 or the corresponding autosomal part of the neo-Z and neo-W chromosomes, and Green-labelled probe of the 45A6 fosmid clone (green signals) to the Z chromosome or the ancestral part of the neo-Z chromosome. Cy3-labelled W-painting probe (yellow signals) highlighted the ancestral part of the neo-W chromosome of S. c. walkeri. Bar=5.0 μm. Arrows, arrowheads, and asterisks indicate the neo-Z chromosome, Z chromosome and chromosome 13, respectively. (a) S. c. walkeri female, (b) S. c. pryeri male, (c) F₁ female, (d) F₁ male, (e, f, i, j) F₂ females and (g, h, k, l) F₂ males. Mitotic metaphase complements of F₂ hybrids were examined in eight males and eight females (Supplementary Table S2). Lower panel: schematic illustrations of sex chromosome constitutions in parents and F₁ and F₂ hybrids from matings between S. c. walkeri females and S. c. pryeri males, based on the FISH results.