Temporalchanges in relative frequencies of third chromosome inversions of Drosophila pseudoobscura in Mexican populations

Variations in relative frequencies of third chromosome inversions during 1974-2000 in three populations of D. pseudoobscura from Mexico were analyzed. The general constitution of these populations is formed from ten up to 15 different inversions, been prevalent, as data shows, the gene arrangements CU, TL, SC, OA, EP, and OL as main components of the studied populations. In Amecameca and Tulancingo we observed that they were constituted by a dominant pair in both cases represented by such partners as CU-TL inside each pair, in Amecameca the superior partner was CU and in Tulancingo TL. In Zirahuen two dominant pairs form the constitution they are SC-OA and CU-TL been the former superior. In all cases sporadic increases of some of inversions were observed. No directional changes were observed. The cyclic pattern is show within periods of 4-5 years.