Aspectos del polimorfismo genético en Drosophila pseudoobscura, D. willistoni y D. nebulosa

in mexico , chromosomal polymorphism in drosophila has been studied in d. pseudoobscura, d. willistoni and d. nebulosa. the first species is better studied with respect to the number of populations analyzed (close to 60), in which there were recognized up to 27 inversions corresponding to the 67.5 % of the total variability for this characteristic, identifying four races. with all of these evidences we rebuilt phylogenetic tree and postulate as ancestral gene arrangement the sequence tree line (tl) and suggesting as origin center of the species the surrounded area between michoacán and zacatecas states. geographical gradients for several inversions at both macro and micro-geographic scales were also detected. the other species were both studied for a seasonal changes during eight years. as a result, it was found a high variability degree for the inversions number, 64.3% of the total variability for this parameter in d. willistoni and 52.9 % in d. nebulosa. average number of inversions carried by a female was 2.57 in d. willistoni and 1.57 in d. nebulosa, which set as marginal with respect to the distribution. nevertheless, they show a considerable variability not expected for a marginal population.