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The species of Odonata are cytogenetically characterised by possessing holokinetic chromosomes, a post-reductional meiosis, an XX/X0 (female/male) sex chromosome mechanism, m-chromosomes, and only one chiasma per bivalent. Chromosome studies were performed on males of Erythrodiplax nigricans and Coryphaeschna perrensi from Argentina. Erythrodiplax nigricans has n=12+XO and lacks m-chromosomes, while C. perrensi has 2n=27, n=13+XO, m-chromosomes and a large autosomal pair associated with the nucleolus. The meiotic behaviour of both species follows the general pattern of the order: the X chromosome is positively heteropycnotic during early prophase I; bivalents regularly show only one chiasma; all chromosomes migrate synchronously and almost parallel to the equatorial plane at anaphase I; at metaphase II the X chromosome is present in all the cells as a consequence of the post-reductional division, lies outside the metaphasic plate, and migrates asynchronously with the autosomes at anaphase II. In C. perrensi, the largest bivalent exhibits two chiasmata in a large proportion of cells, which is a very rare feature among dragonflies. Heterochromatin characterisation with DAPI-CMA banding reveals that C. perrensi does not show fluorescent banding, except for a CMA bright band at one telomeric region of the largest bivalent, associated with the NOR region; in E. nigricans, autosomes have small AT-rich telomeric blocks, except for the smallest pair, which exhibits conspicuous bands in both telomeric regions, one being GC-rich and the other AT-rich. Taking into account that the m-chromosomes have been found in other E. nigricans populations, their absence in the studied population may be due to the presence of such heterochromatic blocks.

caryologia

Fluorescent banding and meiotic behaviour in <i>Erythrodiplax nigricans</i> (Libellulidae) and <i>Coryphaeschna perrensi</i> (Aeschnidae) (Anisoptera, Odonata)

Fluorescent banding and meiotic behaviour in Erythrodiplax nigricans (Libellulidae) and Coryphaeschna perrensi (Aeschnidae) (Anisoptera, Odonata)