A heterozygous paracentric inversion only detectable through Electron Microscopy, in the grasshopper Dichroplus pratensis (Melanoplinae, Acrididae)

Abstract

In this paper we describe a spontaneous heterozygous paracentric inversion in telocentric chromosome L2 of a Dichroplus pratensis male from a natural population of Argentina. This male was also heterozygous for two Robertsonian translocations. The inversion was only detected through transmission electron microscopy of synaptonemal complexes because in some pachytene nuclei a reverse loop was formed and the region distal to it remained unsynapsed. However, in other more advanced pachytene spermatocytes, nonhomologous (straight) pairing, was observed. Instead, analysis of the inversion mutant by light microscopy failed to reveal any pairing abnormalities except for a very low frequency of distal asynapsis of the L2 bivalent. Furthermore, no bridge and fragment configurations were observed nor any other abnormalities during the course of meiosis or the development of spermatids, that could indicate the presence of the inversion. The inversion also causes a significant repatterning of chiasmata in the L2 bivalent which could be due to heterosynapsis and/or desynapsis of the involved region. This could explain the absence of crossing over within the inverted region and thus, of aberrant recombinant chromatids. The relationship between paracentric inversions and Robertsonian translocations in D. pratensis, is discussed as well as the frequency of inversions in natural populations of this species.

Key words:

• Dichroplus pratensis
• paracentric inversion
• Robertsonian translocation
• synaptonemal complex
• grasshopper