Abstract:This review focuses on grasshoppers that are polymorphic for Robertsonian translocations because in these organisms the clarity of meiotic figures allows the study of both chiasma distribution and the orientation of trivalents and multivalents in metaphase I. Only five species of such grasshoppers were found in the literature, and all of them were from the New World: Oedaleonotus enigma (Scudder) (Orthoptera: Acrididae), Leptysma argentina Bruner, Dichroplus pratensis Bruner, Sinipta dalmani Stål, and Cornops … Show more
“…In the case of the bi-armed chromosomes in the common eland, a significant shift in the proximal MLH1 focus position towards the distal end of the SC arm was observed compared to bovine acrocentrics. Similar repression of male meiotic recombination in the proximal regions of bi-armed chromosomes was described in other bovid species (Vozdova et al 2013) as well as in humans (Lian et al 2008) and in mice and insects with Robertsonian fusions Martí and Bidau 2001;Dumas and Britton-Davidian 2002;Colombo 2013;Capilla et al 2014). This fact, together with the overall reduction in the number of the initial DSBs, may explain the significantly lower crossover density (the number of MLH1 foci per micrometer of the SC length) in the common eland compared to cattle.…”
Meiotic recombination between homologous chromosomes is crucial for their correct segregation into gametes and for generating diversity. We compared the frequency and distribution of MLH1 foci and RAD51 foci, synaptonemal complex (SC) length and DNA loop size in two related Bovidae species that share chromosome arm homology but show an extreme difference in their diploid chromosome number: cattle (Bos taurus, 2n = 60) and the common eland (Taurotragus oryx, 2n male =31). Compared to cattle, significantly fewer MLH1 foci per cell were observed in the common eland, which can be attributed to the lower number of initial double-strand breaks (DSBs) detected as RAD51 foci in leptonema. Despite the significantly shorter total autosomal SC length and longer DNA loop size of the common eland bi-armed chromosomes compared to those of bovine acrocentrics, the overall crossover density in the common eland was still lower than in cattle, probably due to the reduction in the number of MLH1 foci in the proximal regions of the bi-armed chromosomes. The formation of centric fusions during karyotype evolution of the common eland accompanied by meiotic chromatin compaction has greater implications in the reduction in the number of DSBs in leptonema than in the decrease of MLH1 foci number in pachynema.
“…In the case of the bi-armed chromosomes in the common eland, a significant shift in the proximal MLH1 focus position towards the distal end of the SC arm was observed compared to bovine acrocentrics. Similar repression of male meiotic recombination in the proximal regions of bi-armed chromosomes was described in other bovid species (Vozdova et al 2013) as well as in humans (Lian et al 2008) and in mice and insects with Robertsonian fusions Martí and Bidau 2001;Dumas and Britton-Davidian 2002;Colombo 2013;Capilla et al 2014). This fact, together with the overall reduction in the number of the initial DSBs, may explain the significantly lower crossover density (the number of MLH1 foci per micrometer of the SC length) in the common eland compared to cattle.…”
Meiotic recombination between homologous chromosomes is crucial for their correct segregation into gametes and for generating diversity. We compared the frequency and distribution of MLH1 foci and RAD51 foci, synaptonemal complex (SC) length and DNA loop size in two related Bovidae species that share chromosome arm homology but show an extreme difference in their diploid chromosome number: cattle (Bos taurus, 2n = 60) and the common eland (Taurotragus oryx, 2n male =31). Compared to cattle, significantly fewer MLH1 foci per cell were observed in the common eland, which can be attributed to the lower number of initial double-strand breaks (DSBs) detected as RAD51 foci in leptonema. Despite the significantly shorter total autosomal SC length and longer DNA loop size of the common eland bi-armed chromosomes compared to those of bovine acrocentrics, the overall crossover density in the common eland was still lower than in cattle, probably due to the reduction in the number of MLH1 foci in the proximal regions of the bi-armed chromosomes. The formation of centric fusions during karyotype evolution of the common eland accompanied by meiotic chromatin compaction has greater implications in the reduction in the number of DSBs in leptonema than in the decrease of MLH1 foci number in pachynema.
“…Although mean values varied between analyses, F1 hybrids/trivalents always exhibited the same distribution pattern: a pronounced decrease in recombination in the proximal regions of the chromosomes compared with St mice/St bivalents. Such modifications in the recombination landscape owing to Rb fusions appear to be a general feature of this type of rearrangement as they have also been observed in a diversity of organisms, that is, shrews, grasshoppers and fish (Borodin et al, 2008;Colombo, 2013;Ostberg et al, 2013). Thus, a growing number of studies demonstrate that heterozygosity for Rb rearrangements is associated with reduced recombination in the proximal regions of chromosomes.…”
Section: Effect Of Rb Heterozygosity On Recombination Patternsmentioning
confidence: 86%
“…As the reduction in Rb heterozygotes is related to meiotic pairing defects in the centromeric region of trivalents (Davisson and Akeson, 1993), the same mechanism cannot apply to Rb bivalents that show conventional pairing patterns (Manterola et al, 2009). Such discrepancies require further assessment to determine the nature of the mechanisms involved in the modifications of recombination patterns (Dumas and Britton-Davidian, 2002;Colombo, 2013;Capilla et al, 2014).…”
Section: Effect Of Rb Heterozygosity On Recombination Patternsmentioning
The recombination suppression models of chromosomal speciation posit that chromosomal rearrangements act as partial barriers to gene flow allowing these regions to accumulate genetic incompatibilities, thus contributing to the divergence of populations. Empirical and theoretical studies exploring the requirements of these models have mostly focused on the role of inversions. Here, the recombination landscape of heterozygosity for Robertsonian (Rb) fusions is investigated in the house mouse. Laboratory-bred F1 males and females between highly differentiated races from Tunisia (Rb: 2n ¼ 22, Standard, St: 2n ¼ 40) were produced in which all Rb fusions are present as trivalents in meiosis. Recombination patterns were determined by the analysis of chiasmata and compared with previous data on the Tunisian parental mice. A comparative analysis was performed on wild-caught male mice spanning the hybrid zone between two Italian races (2n ¼ 40, 2n ¼ 22). The results showed that the chiasma characteristics of both male and female Tunisian F1 and Italian hybrids clearly differed from those of Rb and St mice. Not only was the mean chiasma number (CN) intermediate between those of the parental mice in both geographic samples, but the distribution of chiasmata along the chromosomal arms of the F1 showed a distinct mosaic pattern. In short, the proximal region in the F1 exhibited a reduced CN similar to that observed in homozygous Rb, whereas distal regions more closely matched those in St mice. These results suggest that Rb rearrangements (homozygous or heterozygous) reduce recombination in the proximal regions of the chromosomes supporting their potential role in recombination-mediated speciation models.
“…According to the model of this kind of variation, populations in the center of a species geographic distribution have a higher genetic diversity than those at the margins [31, 32]. This model was observed in the chromosome inversions patterns of Drosophila willistoni , [33], Trimerotropis pallidipennis [34], and Chironomus plumosus [35], and in fusions of Dichroplus pratensis [36]. In the present work, the Santarém population would be central, while the others (Afuá, Rurópolis, Belém, Moju, Acará, Bragança, Santa Bárbara and Benevides) would be marginal.Fig.…”
BackgroundHolocentric chromosomes occur in approximately 750 species of eukaryotes. Among them, the genus Tityus (Scorpiones, Buthidae) has a labile karyotype that shows complex multivalent associations during male meiosis. Thus, taking advantage of the excellent model provided by the Buthidae scorpions, here we analyzed the chromosomal distribution of several repetitive DNA classes on the holocentric chromosomes of different populations of the species Tityus obscurus Gervais, 1843, highlighting their involvement in the karyotypic differences found among them.ResultsThis species shows inter- and intrapopulational karyotype variation, with seven distinct cytotypes: A (2n = 16), B (2n = 14), C (2n = 13), D (2n = 13), E (2n = 12), F (2n = 12) and G (2n = 11). Furthermore, exhibits achiasmatic male meiosis and lacks heteromorphic sex chromosomes. Trivalent and quadrivalent meiotic associations were found in some cytotypes. In them, 45S rDNAs were found in the terminal portions of two pairs, while TTAGG repeats were found only at the end of the chromosomes. In the cytotype A (2n = 16), the U2 snRNA gene mapped to pair 1, while the H3 histone cluster and C
0
t-1 DNA fraction was terminally distributed on all pairs. Mariner transposons were found throughout the chromosomes, with the exception of one individual of cytotype A (2n = 16), in which it was concentrated in heterochromatic regions.ConclusionsChromosomal variability found in T. obscurus are due to rearrangements of the type fusion/fission and reciprocal translocations in heterozygous. These karyotype differences follow a geographical pattern and may be contributing to reproductive isolation between populations analyzed. Our results also demonstrate high mobility of histone H3 genes. In contrast, other multigene families (45S rDNA and U2 snRNA) have conserved distribution among individuals. The accumulation of repetitive sequences in distal regions of T. obscurus chromosomes, suggests that end of chromosome are not covered by the kinetochore.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
