Cytological analysis of a spontaneous translocation heterozygote mosaic in Chorthippus binotatus (Orthoptera, Acrididae)

Abstract

An interchange heterozygote mosaic male of the grasshopper Chorthippus binotatus was found among the 37 individuals analysed from a natural population. The mosaicism of this individual led us to deduce that the L₁ – L₂interchange had place when the testis primordium consisted of about 10 cells. The break points were located at the boundary between the paracentromeric C-bands and the euchromatin of the short arms of both the L₁ and the L₂ chromosomes. The L₁– L₂ interchange did not affect the chiasma formation properties of the L₁ and L₂ bivalents, with the single exception of the L₂ long arm. A significant deficiency of alternate orientations was detected with respect to a randomly orientation of the four centromeres in the multiples. On the other hand, the centromere orientation in the L₁ –L₂ multiples was independent on the chiasma distribution in their different regions. A significantly higher frequency of spermatic macronuclei was observed in the follicles carrying the L₁ – L₂ interchange with respect to those lacking it, but their frequency (1·5 per cent) was insignificant compared with that of the adjacent orientations which are, undoubtedly, the main source of infertility in this male.