Fig. 8. Adult hybrid phenotypes exclude major-effect roles for genes isolated as D. rerio melanophore mutants. (A) Control (wild-type) D. rerioxD. nigrofasciatus hybrids develop adult dorsal and ventral primary melanophore stripes (large arrow) with melanophore numbers similar to those of D. rerio, but with fewer total stripes and fewer melanophores in the secondary melanophore stripes (small arrow) that develop as the fish grow (Parichy and Johnson, 2001). (B) Detail of dorsal primary melanophore stripe. (C) Tester hybrid for the tfap2a (lockjaw) mutant, a sibling to the hybrid in A. Despite the absence of melanophores in tfap2a mutant D. rerio (Knight et al., 2004), tester hybrids have as many melanophores as control hybrids, suggesting that tfap2 does not contribute substantially to the different numbers of melanophores between wild-type D. rerio and D. nigrofasciatus. Minor individual variation in secondary melanophore and stripe numbers does not segregate with tfap2 alleles (data not shown). (D) Detail of dorsal primary melanophore stripe in tester hybrid, showing a similar number of melanophores to the control in B.