| Sumario: | Two populations of Sinipta dalmani (2n = 23, XO ♂/XX ♀) from Entre Ríos Province (Argentina) are polymorphic for a pericentric inversion in pair M4 The inverted segment occupies about 40% of the chromosome lenght and changes its morphology from acrocentric to submetacentric. The frequencies of karyomorphs in each population are fitted to the expected according Hardy Weinberg's equilibrium. The inversion does not alter the mean total chiasma frequency. However, there is a significant decrease in interstitial chiasma frequency in the homozygous condition. Such decrement may be explained by a redistribution of chiasmata in medium sized bivalents. In the pair M4 the inversion precludes the crossing over within its limits in the heterozygous condition and increases terminal chiasma frequency in homozygosis. In the rest of the medium pairs, there is a significant decrease in interstitial chiasma frequency and a significant increase in proximal and distal chiasma frequencies in both heterozygous and homozygous individuals. It is concluded that this pericentric inversion affects intra and interchromosomally the level of recombination. © 1989 Taylor & Francis Group, LLC.
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