whereas symmetric allelic expression in F1 hybrid should be observed if the trans-regulation diverges between species (Fig. 4D, supporting information Fig. S3).
We checked the specificity of each species-specific YRG probe in P. xuthus and P. polytes samples. The Px-YRG probe detected only P. xuthus mRNA, whereas the Pp-YRG probe detected only P. polytes mRNA (Fig. 4E). We next analyzed F1 hybrid specimens by dividing the larval epidermis in half along the midline and compared the expression pattern be- tween sides. We used the Px-YRG probe in the left-side sam- ples, and Pp-YRG probe in the right-side samples (Fig. 4E). Both Px-YRG and Pp-YRG detected a similar expression pat- tern (Fig. 4E). The non-expressing region of the V-shaped boundary of Px-YRG was obscure, which is consistent with the F1 hybrid phenotype (Fig. 4B). In the V-shaped region, Pp-YRG expression was detected although it was slightly weaker than in the presumptive green region