Descripción: Pseudacteon flies, parasitoids of worker ants, are being intensively studied as potentially effective agents in the biological control of the invasive pest fire ant genus Solenopsis (Hymenoptera: Formicidae). This is the first attempt to describe the karyotype of P. curvatus Borgmeier, P. nocens Borgmeier and P. tricuspis Borgmeier. The three species possess 2n = 6; chromosomes I and II were metacentric in the three species, but chromosome pair III was subtelocentric in P. curvatus and P. tricuspis, and telocentric in P. nocens. All three species possess a C positive band in chromosome II, lack C positive heterochromatin on chromosome I, and are mostly differentiated with respect to chromosome III. P. curvatus and P. tricuspis possess a C positive band, but at different locations, whereas this band is absent in P. nocens. Heterochromatic bands are neither AT nor GC rich as revealed by fluorescent banding. In situ hybridization with an 18S rDNA probe revealed a signal on chromosome II in a similar location to the C positive band in the three species. The apparent lack of morphologically distinct sex chromosomes is consistent with proposals of environmental sex determination in the genus. Small differences detected in chromosome length and morphology suggests that chromosomes have been highly conserved during the evolutionary radiation of Pseudacteon. Possible mechanisms of karyotype evolution in the three species are suggested. Copyright © 2009, Sociedade Brasileira de Genética.

Descripción: The haploid DNA content of Aeshna confusa (2n = 27, n = 13 + XO, male). A. bonariensis (2n = 26, n = 12 + neo-XY, male) and A. cornigera planaltica (2n = 16, n = 7 + neo-XY, male) has been determined (2.16 ± 0.16 pg, 1.81 ± 0.17 pg, and 2.08 ± 0.08 pg, respectively). Despite the differences in chromosome size and number, differences in DNA content between species are not significant. The karyotypic analysis of Aeshna species leads to the conclusion that fusions between autosomes or autosome and the sex chromosome, are the only chromosome rearrangement that occurred during evolution. In the species here studied, fusions have taken place with a minimal loss of DNA; however, other species of the genus show important differences in genome size, which cannot only be justified by fusion events.

Descripción: Previous works in a colonized and an original population of Drosophila buzzatii have shown a consistent relationship between the inversion polymorphism and thorax length, a measure of body size. However, the populations studied in those reports share a close genealogical relationship as suggested by several lines of evidence. In the present paper, we revisit this issue by analysing the correlation between second chromosome arrangements and thorax length in two Argentinian natural populations (Termas de Rio Hondo and Arroyo Escobar) from different biogeographic areas with different host plants. Our findings are: (1) inversion frequencies were significantly different between populations; (2) the mean thorax length of flies collected in both populations was not significantly different; and (3) we obtain confirming evidence that flies carrying 2st, the ancestral gene order, have on average a smaller body size than those carrying the derived arrangements (2j and 2jz3). These results suggest that the biometrical effect of inversions on body size previously described are due to genetic differences between arrangements and not to the close historical relationship between the populations studied in previous reports.

Descripción: Erythrodiplax is an American genus of dragonflies with a mainly neotropical distribution and with 19 species cited in Argentine. In this work 9 species have been chromosomically analyzed: E. atroterminata, E. connata fusca, E. corallina, E. lygaea, E. media, E. melanorubra, E. nigricans, E. ochraceae and E. umbrata. All of them, except E. media, have n = 12 + X in males, with a similar karyotype and meiotic behaviour. Bivalents decrease gradually in size, except for the small m bivalent, whose size varies among the species. The X chromosome in E. corallina, E. lygaea, E. nigricans and E. umbrata is twice as large as in the other 4 species. On the other hand, E. media has n = 10 + neo-XY, m chromosomes, and its karyotype characterizes by the presence of two large bivalents (being the largest the heteromorphic neo-XY). The genus Erythrodiplax presents a great karyotypic constancy, although polytypisms for the m chromosome size have been detected in E. atroterminata, E. connata fusca and E. umbrata, and for the sex chromosome determining system, in E. media. The chromosome rearrangements that probably originated these polytypisms, and their evolutionary importance are discussed.

Descripción: The cactophilic Drosophila buzzatii provides an excellent model for the study of reaction norms across discrete environments because it breeds on rotting tissues (rots) of very different cactus species. Here we test the possible effects of second chromosome inversions on body size and shape (wing loading) across suitable natural breeding substrates. Using homokaryotypic stocks derived from several lines homozygous for four naturally occurring chromosomal inversions, we show that arrangements significantty affect size-related traits and wing loading. In addition, karyotypes show differing effects, across natural breeding resources, for wing loading. The 2st and 2jz3 arrangements decrease and the 2j arrangement increases wing loading. For thorax length and wing loading, karyotypic correlations across host plants are slightly lower in females than in males. These results support the hypothesis that these traits have a genetic basis associated with the inversion polymorphism.

Descripción: This paper presents the karyotype and DNA content of 12 diploid species of Hippeastrum from South America. The variation in genome size is compared with the karyotype and DNA content of Amaryllis belladonna from South Africa. The Hippeastrum species present a uniform and bimodal basic karyotype formula, but significant differences are found in the total chromosome volume (TCV) and nuclear DNA content. A positive correlation between the DNA content and TCV is also observed. The karyotype's constancy is a product of changes in DNA content occurring in the whole chromosome complement. The DNA addition to the long and short sets of chromosomes varies independently. In species with higher DNA contents, the short chromosomes add equal DNA amounts to both arms, maintaining their metacentric morphology, whereas the long chromosomes add DNA only to the short arm, increasing the chromosome symmetry. These data show that the evolutionary changes in DNA amount are proportional to chromosome length, maintaining the karyotypic uniformity. A. belladonna has a larger DNA content and possesses a karyotype different from that of Hippeastrum spp., supporting the distinction between the two genera and upholding the name Amaryllis for the South African entity against Hippeastrum for the South American genus. © 2007 The Linnean Society of London.

Descripción: This paper presents the karyotype, DNA content and meiotic behaviour of five species of Vicia from Argentina (V. macrograminea Burk., V. graminea SM., V. epetiolaris Burk., V. pampicola Burk. and V. nana Vog.). All the species have the same chromosome number and karyotype formula (2n = 14; 6 m + 4 st + 4 t). Each species, however, displays a characteristic number and position of the nucleolar organizer region (NOR) and different sizes of the respective satellites, confirmed by Ag-NOR banding. Moreover, significant differences were found in the total chromosome volume (TCV) and DNA content of the species. Positive correlations between DNA content and TCV, and between DNA content and type of life cycle were also found. TCV and DNA content are lower in V. nana (annual) and higher in V. macrograminea (biennial-perennial). The material displayed marked karyotypic orthoselection, with similar karyotypes in all studied species, even when the overall chromosome size varied. Evolutionary changes in DNA amount are proportional to the relative length of each chromosome arm, maintaining karyotypic uniformity. Significant differences were found between the meiotic behaviour of V. graminea and that of the other species. V. graminea has a lower frequency of ring bivalents and chiasmata per cell, and also has a lower interstitial chiasma frequency. In general, the results are congruent with the morphological data reported for these species.

Descripción: Fil:Poggio, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: By using improved pulsed field gel electrophoresis conditions, the molecular karyotype of the reference clone CL Brener selected for Trypanosoma cruzi genome project was established. A total of 20 uniform chromosomal bands ranging in size from 0.45 to 3.5 Megabase pairs (Mbp) were resolved in a single run. The weighted sum of the chromosomal bands was approximately 87 Mbp. Chromoblots were hybridized with 39 different homologous probes, 13 of which identified single chromosomes. Several markers showed linkage and four different linkage groups were identified, each comprising two markers. Densitometric analysis suggests that most of the chromosomal bands contain two or more chromosomes representing either homologous chromosomes and/or heterologous chromosomes with similar sizes.

Descripción: Twenty-one native populations (1120 individuals) of maize from Northern Argentina were studied. These populations, which belong to 13 native races were cultivated at different altitudes (80-3620 m). Nineteen of the populations analyzed showed B chromosome (Bs) numerical, polymorphism. The frequency of individuals with Bs varied from 0 to 94%. The number of Bs per plant varied from 0 to 8 Bs, with the predominant doses being 0, 1, 2, and 3. Those populations with varying number of Bs showed a positive and statistically significant correlation of mean number of Bs with altitude. The DNA content, in plants without Bs (A-DNA)(2n = 20), of 17 populations of the 21 studied was determined. A 36% variation (5.0-6.8 pg) in A-DNA content was found. A significant negative correlation between A-DNA content and altitude of cultivation and between A-DNA content and mean number of Bs was found. This indicates that there is a close interrelationship between the DNA content of A chromosomes and doses of Bs. These results suggest that there is a maximum limit to the mass of nuclear DNA so that Bs are tolerated as long as this maximum limit is not exceeded.

Descripción: It is universally true in ecological communities, terrestrial or aquatic, temperate or tropical, that some species are very abundant, others are moderately common, and the majority are rare. Likewise, eukaryotic genomes also contain classes or "species" of genetic elements that vary greatly in abundance: DNA transposons, retrotransposons, satellite sequences, simple repeats and their less abundant functional sequences such as RNA or genes. Are the patterns of relative species abundance and diversity similar among ecological communities and genomes? Previous dynamical models of genomic diversity have focused on the selective forces shaping the abundance and diversity of transposable elements (TEs). However, ideally, models of genome dynamics should consider not only TEs, but also the diversity of all genetic classes or "species" populating eukaryotic genomes. Here, in an analysis of the diversity and abundance of genetic elements in >500 eukaryotic chromosomes, we show that the patterns are consistent with a neutral hypothesis of genome assembly in virtually all chromosomes tested. The distributions of relative abundance of genetic elements are quite precisely predicted by the dynamics of an ecological model for which the principle of functional equivalence is the main assumption. We hypothesize that at large temporal scales an overarching neutral or nearly neutral process governs the evolution of abundance and diversity of genetic elements in eukaryotic genomes. © 2013 Serra et al.

Descripción: Three populations of Artemia from La Pampa Province, Argentina, were cytogenetically analyzed: Salinas Grandes de Hidalgo, Laguna Callaqueo, and Laguna Colorada Chica. Both mitotic and male meiotic chromosomes were studied. All 3 populations share the same diploid (2n = 44) and/or haploid chromosome number (n = 22), and hence were determined as Anemia persimilis Piccinelli and Prosdocimi. Although bivalents decrease gradually in size, differences among the larger and the smaller ones were apparent. So far, no cytogenetic differences have been detected among the 3 populations. Chromosomes with metacentric, submetacentric, and telocentric morphology were detected in mitotic prometaphase cells, suggesting that chromosomes of Anemia may be monocentric.