Spontaneous chromosome mutations in Truxaline grasshoppers.

Abstract

Three distinct mutant conditions are described in single male individuals from three species of short horn grasshopper. Of these, one is an entire germ line mutant of Myrmeleotettix maculatus, heterozygous for a centric fusion between single M4 and M5 telocentric chromosomes. In contrast, the remaining two mutants are present in mosaic form. One is heterozygous for an L1-M4 interchange in Omocestus viridulus, the other tetrasomic for the M4 chromosome in Chorthippus parallelus which in addition is characterised by the inclusion of a supernumerary heterochromatic segment on one S8 homologue. Centric fusion in Myrmehotettix maculatus has neither disturbed the chiasma potential of the elements constituting the fusion multiple nor, has it apparently influenced the production of balanced gametes. The pattern of chiasma formation in the L1-M4 interchange multiple lends support to the contention that the process of chiasma formation originates near the distal end of chromosome arms in Omocestus viridulus. There is no interaction between the two mutant conditions of tetrasomy and the presence of supernumerary segments in Chorthippus parallelus. Moreover, because of the precocious nature of two of the four M4 homologues there is little tendency to form multivalents. The two M4 bivalents share a similar mean chiasma frequency.