(a–h) HH27 wing-polarizing region grafted to posterior and anterior of HH20 wings (a) express Shh after 32 h (arrows, b,e, n=11/13). Wings with posterior grafts normal (c,d, n=2/3—one lost digit 3), wings with anterior graft duplicated* (f,g, n=10/12). After 24 h, 62% of cells in G1 phase in grafted polarizing regions (n=10) compared with 60% in contralateral wings (h, n=10). (i–p) HH24 wing-polarizing region serially grafted (twice) to posterior and anterior of HH20 wings (i) express Shh after 32 h (arrows, j,m, n=3/3). Wings with posterior grafts normal (k,l, n=2/2), wings with anterior grafts duplicated* (n,o, n=2/3). After 24 h, 62% of cells in G1 phase in grafted polarizing regions (n=10) compared with 59% in contralateral wings (p, n=10). (q–x) HH27 wing-polarizing region grafted to posterior or anterior of HH24 wings (q), Shh not expressed after 16 h (arrows, r,u, n=15/15). Wings with posterior graft normal (s,t, n=3/3), wings with anterior graft have duplicated digit 1* (v,w, n=2/4—two not duplicated). After 24 h, 79% of cells in polarizing regions (n=12) in G1 phase compared with 78% in contralateral wing bud-polarizing regions (x, n=12). In h,p and x there is a significant difference in G1 numbers between host values and expected values for the stage of the donor polarizing region (Pearson’s χ2 test—P<0.05) consistent with cell cycle parameters of the graft being reset close to host levels (see also ). Scale bars, 500 μm (b,e,j,m), 750 μm (r,u), 1 mm (c,d,f,g,k,l,n,o,s,t,v,w).