**3.5.1 Crosses between** *D. mulleri* **and** *D. mojavensis*

The cross between *D. mulleri* and *D. mojavensis* showed asymmetric isolation, with many descendents only in the direction of *D. mulleri* females and *D. mojavensis* males. The reciprocal cross did not produce offspring despite the presence of courtship among couples and eggs in the plate. The hybrid larvae were analyzed in 10% PAGE and showed threeband patterns for EST-4 and EST-5 (Figure 4). For both enzymes, the slower band corresponded to the enzyme encoded by *D. mulleri* and the faster to the enzyme encoded by *D. mojavensis*. The intermediate band represented a hybrid enzyme, indicating that EST-4 and EST-5 are dimeric in both species.

For EST-4, the hybrid intermediate bands were located closer to the band encoded by *D. mulleri*, which could be a result of differences in the I.P. values of theses enzymes (Table 3). The same was not observed for EST-5, as this enzyme has nearly the same value for both of these species.
