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Effects of centric fusions on chiasma frequency and position in Leptysma argentina (Acrididae: Orthoptera) I. Spontaneous and stable polymorphic centric fusions

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Abstract

Leptysma argentina is a highly polymorphic South-American grasshopper from the cytological point of view; all populations so far studied carry a polymorphic fusion between pairs 3 and 6. In heterozygotes, the trivalent 3-3/6-6 shows alternate orientation in 97.17% of the cells. Trivalent chiasma frequency is significantly lower than in the combined 3 and 6 bivalents of the standard homozygote; besides, there is a marked displacement of chiasmata to a distal position. In structural homozygotes the same effects, but not so marked, were observed.

One individual was a double heterozygote for both the polymorphic centric fusion and a spontaneous one between pairs 5 and 7. The presence of a fragment, sometimes associated with the centromeric region of the nonfused 5 chromosome, was detected in more than 50% of the cells. The orientation of trivalent 5-5/7-7 in metaphase I was highly irregular (36% linear orientation). Neither frequency nor position of chiasmata were altered in trivalent 5-5/7-7 when compared with bivalents 5+7 of normal individuals.

The results suggest that proximal and interstitial chiasma reduction observed in trivalent 3-3/6-6 of L. argentina is due to a later adaptation to the polymorphic condition or a fortuitous genetic condition present in the original mutant, rather than to a direct effect of the fusion itself on chiasma distribution.

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  1. Laboratorio de Genética, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, 1428, Buenos Aires, República Argentina

    P. C. Colombo

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  1. P. C. Colombo
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Colombo, P.C. Effects of centric fusions on chiasma frequency and position in Leptysma argentina (Acrididae: Orthoptera) I. Spontaneous and stable polymorphic centric fusions. Genetica 72, 171–179 (1987). https://doi.org/10.1007/BF00116220

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  • DOI: https://doi.org/10.1007/BF00116220

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