Figure 7. A developmental model for the observed phenotypic effects of the alleles at the Sd locus on the black pattern of the forewing.

(A) The arrangement of organizing centers for Heliconius wing patterns. Lower case letters indicate serially homologous organizing centers (Nijhout and Wray 1988). The organizing centers control development of the black parts of the color pattern. The dotted line, delimit a hypothetical region (shaded) that represent s the influence of the two QTLs (Sd = WntA and possibly Ro color pattern genes) that control the upper forewing H. e. notabilis patch (see Figure 6). The Sd black melanization pattern is centered on the d and f NGP elements while the Ro melanization pattern coincide with the h NGP elements. (B) Expansion of the black pattern controlled by each of the Sd alleles. Each allele controls a different aspect of pattern expansion from organizing centers d and f. The Sd^era allele also controls melanization along the wing veins, which breaks up the colored background pattern into discrete patches. The hypothetical region of action for the Sd and Ro color pattern genes is shown as well for the individual H. erato races.