A G banding technique combining trypsin and hot saline treatments was used to analyze the chromosomes of two grasshopper species, Eyprepocnemis plorans and Locusta migratoria, both of which contain both standard and supernumerary heterochromatin. Although this technique does not produce G bands like those in mammalian chromosomes, it serves to characterize heterochromatic regions whose nature has been inferred from other banding techniques (C, N, CMA, and DAPI banding). The light regions revealed by G banding contain GC-rich DNA sequences, the more prominent of which coincide with nucleolus organizer regions (NORs). Furthermore, the proximal heterochromatin in E. plorans was heterogeneous, and the standard and supernumerary heterochromatin showed conspicuous differences in organization. Supernumerary heterochromatin is an exception to the regular patterns shown by the standard heterochromatin. The findings are related to the mechanism of action of these banding techniques.Key words: banding techniques, grasshoppers, Eyprepocnemis plorans, Locusta migratoria.

/n and tDepartamento de Genét/ca, Facultad de B/o/ogIa, Un/vers/dad Comp/utense de Madrid, E-28040 Madrid, Spa/n Twenty-eight progeny analyses (PAs) performed on specimens of E. plorans collected from four natural Iberian populations have been informative about the transmission of rare B chromosome types or the de novo origin of some of them. At least ii rare B-types have been found in addition to the predominant ones: B1 in Daimuz, B2 in Jete and Salobreña, and B5 in Fuengirola. The presence in two controlled crosses of one embryo carrying a B-type which was absent in the parents suggests that these B variants (B20 and B ) have originated de novo. Eleven other PAs suggest that new B derivatives are recurrently arising in these populations. The most frequent B chromosome mutation was centromere misdivision that originated four different B-types (B2m1, B110, B210 and Bmjnj). Other rearrangements were pericentric inversions (B211, B212 and B213), inverse tandem fusion (B211), centric fusion (B11) and deletions (B2d1 and B2d2). The four B derivatives produced by centromeric misdivision are significantly eliminated during sexual transmission, most probably owing to deficiencies in the control of chromosome movement by their hemicentromeres. Those derived from translocations showed Mendelian transmission but deletion B variants showed a tendency to elimination. Our results suggest that B chromosome substitution of B1 by B2 in the Salobreña and Jete populations could be achieved by differences in relative transmission efficiency, as in one controlled cross, where the female carried 1 B1 plus 1 B2, B2 was significantly overtransmitted and B1 eliminated.

The response of 11 supernumerary segments to C-banding has been compared in six species of grasshoppers. A unique euchromatic supernumerary segment was present in the five populations of Omocestus bolivari analysed. It appears negatively heteropycnotic during the first prophase of meiosis and does not C-band. This euchromatic segment is distally located in the M6 chromosome and in every case was present in a heterozygous condition. It does not associate with the telomere of its unsegmented homologue and, consequently, the unequal M6 bivalents always segregate equationally for the extra segment in the first meiotic division. This euchromatic segment does not influence mean cell chiasma frequency but does influence chiasma position in the M6 bivalents carrying it. Four additional types of heterochromatic supernumerary chromosome segments may be distinguished in grasshoppers by C-banding: a) those darkly C-banded, b) those partly darkly C-banded, c) those lightly C-banded and d) those which do not C-band. All five types of segment appear to affect chiasma distribution in heterozygous monochiasmate bivalents but only those heterochromatic segments that do not C-band influence mean cell chiasma frequency.

Mitotic instability of B chromosomes during embryo development has been studied in the locust Locusta migratoria. Direct cytological observation of B chromosome nondisjunction in embryos has shown that it occurs in 2.7 per cent of anaphase and telophase cells, and that this frequency is not significantly different among embryos of 5-9 days of development. We have defined three indices which have been shown to be very useful to quantifying mitotic instability: R, the ratio of embryos showing B chromosome instability, M, the median of the distribution of B chromosome numbers in a sample of embryo cells, which has been shown to be a good estimator of the original number of B chromosomes present in the zygote, and MI, the sum of all deviations (in absolute value) of B numbers with respect to M in the same embryo. Mitotic instability of B chromosomes is already apparent in 3-day-old embryos and reaches its maximum value on the fifth day of development. The intensity of mitotic instability, as measured by MI, varies significantly during the developmental period analysed but no definite trend was observed.

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