Position Of Chiasmata Research Articles

The challenge of evolving stable polyploidy: could an increase in "crossover interference distance" play a central role?

Whole genome duplication is a prominent feature of many highly evolved organisms, especially plants. When duplications occur within species, they yield genomes comprising multiple identical or very similar copies of each chromosome (“autopolyploids”). Such genomes face special challenges during meiosis, the specialized cellular program that underlies gamete formation for sexual reproduction. Comparisons between newly formed (neo)-autotetraploids and fully evolved autotetraploids suggest that these challenges are solved by specific restrictions on the positions of crossover recombination events and, thus, the positions of chiasmata, which govern the segregation of homologs at the first meiotic division. We propose that a critical feature in the evolution of these more effective chiasma patterns is an increase in the effective distance of meiotic crossover interference, which plays a central role in crossover positioning. We discuss the findings in several organisms, including the recent identification of relevant genes in Arabidopsis arenosa, that support this hypothesis.Electronic supplementary materialThe online version of this article (doi:10.1007/s00412-015-0571-4) contains supplementary material, which is available to authorized users.

Deep cytogenetics analysis reveals meiotic recombination depletion in species of Senecio (Asteraceae).

BackgroundSenecio is the largest genus in the Asteraceae family growing in all environments around the world. It displays taxonomic and systematical difficulties. Cytogenetic knowledge of this genus is ancient, scarce and mainly restricted to chromosome number records.ResultsIn this study we analyzed chromosome number, meiotic configuration, bivalent morphology, meiotic behavior and pollen grain stainability on 100 accessions of 27 different polyploid Senecio L. sect Senecio entities. Median, standard deviation and mode were calculated for number and position of chiasmata and meiotic recombination was statistically evaluated. Although high frequency of multivalents and associated meiotic irregularities are expected in high polyploids, bivalents predominance and, consequently, regular meiosis were observed, with normal sporogenesis and high pollen grain stainability.ConclusionDepletion in the total chiasmata was significant only in some species but the terminal position was preferential in all the entities analyzed, indicating significant reduction in recombination. The regular meiosis observed suggest that intra and intergenomic reorganization process occur quickly and efficiently in this genus. Mechanisms of diploidization, common to all polyploids, are reinforced by the strong reduction in crossing-over rushing polyploids stabilization.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-20) contains supplementary material, which is available to authorized users.

Genetic Recombination Potential ofGonipterus scutellatus(Gyllenhal) (Coleoptera: Curculionidae), a Pest of Eucalyptus Plantations in South Africa

The eucalyptus snout beetle, Gonipterus scutellatus (Gyllenhal), introduced to South Africa from Australia, causes extensive damage to eucalyptus plantations in colder regions where biological control is less effective. A cytogenetic study was undertaken to assess the weevil's genetic recombination potential and thereby its ability to adapt to changing environmental conditions. During this study we investigated: (i) the sequence of meiosis; (ii) the weevil's karyotype; and (iii) the number and position of chiasmata on the bivalents. Squashes of male testes revealed a normal, chiasmate meiosis, a sex chromosome complement of Xyp and an autosome complement of three large, and two medium-sized, sub-metacentric pairs and seven small acrocentric pairs. The diploid chromosome number (2n = 26) is marginally higher than the ancestral chromosome number of the Curculionidae (2n = 22). Chiasmata were absent from the proximal regions of the bivalents, occurring mostly in the distal regions and less frequently in the ...

An algorithm for determining the origin of trisomy and the positions of chiasmata from SNP genotype data

Trisomy causes mental retardation, pregnancy loss, IVF failure, uniparental disomy and several other pathologies, and its accurate detection is thus clinically essential. Most trisomies arise at meiosis I and are associated with increasing maternal age and reduction or alteration in recombination patterns. Investigations into the relationship between trisomy and meiotic recombination have used short tandem repeat markers; however, this approach is limited by the resolution with which the position of crossovers can identified. As cytogenetics enters the post-genomic era, recent work has used array comparative genomic hybridisation (aCGH) to screen for trisomy of all 24 chromosomes, determining chromosome copy number by dosage analysis. However, aCGH has a fundamental drawback for studying the aetiology of trisomy since neither the parent and phase of origin nor uniparental disomy can be ascertained. The development of SNP microarrays has made it possible to analyse multiple loci for sequence variation, and the proprietary software provided can determine the presence of aneuploidy by algorithms based on fluorescence intensity. To the best of our knowledge, however, such software is not equipped to determine the phase of origin of the error or the position of any chiasmata. In this study, therefore, we present an algorithm to determine the parent of origin, the phase of origin and the location of chiasmata in a series of nine "trisomy triplets" (i.e. samples derived from father, mother and their trisomic foetus). Novel adaptations of well-established principles are applied along with a simple algorithm written in Microsoft Excel for visualisation of the results. Such analysis has a range of applications in preimplantation and prenatal diagnosis.

Metaphase I orientation of Robertsonian trivalents in the water-hyacinth grasshopper, Cornops aquaticum (Acrididae, Orthoptera)

Trivalents resulting from polymorphic Robertsonian rearrangements must have a regular orientation in metaphase I if the polymorphisms are to be maintained. It has been argued that redistribution of proximal and interstitial chiasmata to more distal positions is necessary for a convergent orientation, the only one that produces viable gametes. Cornops aquaticum is a South-American grasshopper that lives and feeds on water-hyacinths, and has three polymorphic Robertsonian rearrangements in its southernmost distribution area in Central Argentina and Uruguay. The orientation of trivalents in metaphase I, the formation of abnormal spermatids and the frequency and position of chiasmata in the trivalents, was analysed in a polymorphic population of C. aquaticus. In this study we observed a correlation between the number of trivalents with the frequency of abnormal spermatids; additionally, the number of chiasmata, especially proximal and interstitial ones, was strongly correlated with the frequency of the linear orientation. Therefore we confirmed our previous assumption, based on other evidence, that the chiasmata redistribution in fusion carriers is essential to the maintenance of the polymorphisms.

Variability along a latitudinal gradient in the chiasma frequency and morphological characters of Dichroplus pratensis (Orthoptera: Acrididae)

The grasshopper Dichroplus pratensis Bruner is polymorphic and polytypic for a complex Robertsonian system. In this species, centric fusions induce changes in number and position of chiasmata, and thus potentially affect intrachromosomal genetic recombination and genetic variability. Males and females, from 23 populations covering most of the geographic range of the species and spanning 22 degrees of latitude, were studied. We analyzed chiasma frequency in relation to variability in six exomorphological characters. The chromosomal polymorphisms of D. pratensis are widely geographically distributed, and show a central-marginal pattern, in which the central populations (those occupying the ecologically optimal habitats) have high mean frequencies of different fusions per individual (F) of up to F = 3.00 and total chiasma frequencies as low as XT = 8.98 per cell, while those near the margins of the distribution (central Patagonia and the Andes) have very low levels of chromosomal polymorphisms [down to F = 0.00 in most geographically marginal locations), monomorphic karyotypes and high chiasma frequencies (XT = 11.66, in the southernmost (Rada Tilly, 45°57´S) and XT = 12.01 in the northernmost population (Volcan, 23°55´S)]. Increasing chiasma frequencies towards the margins of the range are positively and significantly correlated with increasing levels of morphological variability. The decrease in fusion polymorphism and the consequent increase in genetic recombination (both inter- and intrachromosomal) in the marginal areas, is a result of natural selection favouring higher levels of variability, which could be adaptive in ecologically harsher and changing environments.

Meiotic Pairing and Chiasma Frequency in an Induced Trisomic of Grass Pea (Lathyrus sativus L.)

Meiotic pairing association and chiasma frequency were studied in a gamma-ray induced primary trisomic of grass pea (Lathyrus sativus L.). The trisomic was identified by phenotypic abnormalities, early maturity and presence of an extra chromosome (2n+1=15), while occurrence of 7 bivalents was the usual feature in normal diploids (2n=14). In the trisomic, formation of a univalent was more common than that of a trivalent, although bivalent association was predominant. Ring bivalents appeared more frequently than chain or rod configurations. Terminalization of 2 chiasmata in the 2 arms may give rise to ring bivalent, while a single chiasma may terminalize to form a chain. In the trisomic, frequent occurrence of linear or frying pan configuration and occasionally Y-shaped trivalent formation indicated unmodified nature of the extra chromosome; this characterized it as a primary trisomic. Terminalization of chiasmata in both the arms of a chromosome involving its 2 homologous partners may result in linear configuration, while a chiasma in the distal end with another chiasma in the same arm may give rise to frying pan configuration, but an interstitial chiasma accompanied with another chiasma formed at the terminal position distal to former might form Y-shaped trivalent. Configuration of trivalent may thus be influenced by the number and position of chiasmata. Compared to normal diploids chiasma frequency reduced in the trisomic. More frequent occurrence of unequal anaphasic separation of chromosomes may be attributed to reduced pollen fertility in the trisomic.

Sex incidences of chiasmata variation in respect of position, distribution and frequency in some important legumes and grasses

Abstract To find out whether the chromosomes behave in the similar fashion in two sex mother cells i.e. the pollen mother cells (PMCs) and the embryo sac mother cells (EMCs) in the bisexual plants, 13 species (19 accessions) of the families Fabaceae (7 spp; 12 acc.) and Poaceae (6 spp; 7acc.), were studied for male and female meiosis, ten (14acc.) being studied for the first time. The present study brought to light several facts not recorded earlier. Asynchrony was observed in the behaviour of chromosomes in the two sex cells with respect to the frequency, distribution and position of chiasmata. While a higher chiasmata frequency was recorded in the pollen mother cells (PMCs) of Lathyrus odoratus, L. sativus, L. aphaca, Lupinus albus and Pisum sativum, in species like Lolium perenne, L. multiflorum and Hordeum vulgare a reciprocal situation existed. Further, in L. perenne and L. multiflorum while bivalents showed distally localized chiasmata in the PMCs, in EMCs their distribution was random. However, in Vicia faba, Phaseolus vulgaris, Secale cereale, Lolium temulentum and Phalaris minor absence of a sex difference in meiosis was noted. Significant differences also existed in the bivalent size of the two sex cells in Lathyrus odoratus, L. sativus, V. faba and H. vulgare. In all these species, barring H. vulgare, the bivalent size was bigger in the PMCs studied. In H. vulgare a reverse situation existed. Sex difference in meiosis was distinctly evident in Lupinus albus. Of the two populations studied while one population showed synchronous behaviour of chromosomes in the two sex cells, the other population although showed normal microsporogenesis, its megasporogenesis was abnormal (desynaptic) being characterized by the failure of synapsed chromosomes to retain chiasmata in 61.11 per cent cells at diakinesis. It is concluded that the contribution of the two sex cells towards generating variability through recombination is not the same. In desynaptic L. albus while the effective recombination is brought about by the male meiosis, the female sex cells provide for the retention of certain linkage groups. The possible cause(s) and the significance of differential behaviour of chromosomes in the two sex mother cells of different species studied is discussed.

Phosphorylated proteins are involved in sister-chromatid arm cohesion during meiosis I.

Sister-chromatid arm cohesion is lost during the metaphase I/anaphase I transition to allow homologue separation. To obtain needed information on this process we have analysed in grasshopper bivalents the sequential release of arm cohesion in relation to the behaviour of chromatid axes. Results show that sister axes are associated during early metaphase I but separate during late metaphase I leading to a concomitant change of chromosome structure that implies the loss of sister-kinetochore cohesion. Afterwards, homologues initiate their separation asynchronously depending on their size, and number and position of chiasmata. In all bivalents thin chromatin strands at the telomeres appeared as the last point of contact between sister chromatids. Additionally, we have analysed the participation of phosphoproteins recognised by the MPM-2 monoclonal antibody against mitotic phosphoproteins in arm cohesion in bivalents and two different kinds of univalents. Results show the absence of MPM-2 phosphoproteins at the interchromatid domain in mitotic chromosomes and meiotic univalents, but their presence in metaphase I bivalents. These phosphoproteins are lost at the onset of anaphase I. Taken together, these data have prompted us to propose a 'working' model for the release of arm cohesion during meiosis I. The model suggests that MPM-2 phosphoproteins may act as cohesive proteins associating sister axes. Their modification, once all bivalents are correctly aligned at the metaphase plate, would trigger a change of chromosome structure and the sequential release of sister-kinetochore, arm, and telomere cohesions.

Chiasma distributions and chromosome segregation in male and female translocation heterozygous mice analysed using FISH.

Two factors postulated to influence the meiotic behaviour of reciprocal translocations were investigated. Firstly, variation in the length of translocated and non-translocated segments was studied in male mice using four different rearrangements involving chromosomes 2 and 4. Secondly, sex-related effects were analysed through comparison of the meiotic behaviour of two translocations in male and female germ cells. In the first part of the study, primary and secondary spermatocytes of male mice carrying a translocation [T(2;4)1Ca, T(2;4)13H, T(2;4)1Sn, or T(2;4)1Go] were screened. Each rearrangement had different proportions of cells with ring and chain quadrivalents at metaphase I; the T(2;4)1Sn heterozygote also had a high rate (45%) of translocation bivalents. In general, the translocations had elevated chiasma frequencies in the rearranged chromosomes compared with structurally normal chromosomes 2 and 4, although the extent of the effect varied. Each rearrangement produced a different array of segregation products at metaphase II, reflecting their contrasting frequencies of multivalent configurations at metaphase I. Comparison of chromosome behaviour at metaphase I and II suggested that certain configurations tended to adopt particular orientations. However, it was also clear that such correlations were imprecise and that other factors, possibly the exact positions of chiasmata, also played a role in multivalent orientation. Two rearrangements, T(2;4)1Go and T(7;16)67H, were analysed in female mice. The frequencies of the various multivalent types at metaphase I differed from those in male carriers of these rearrangements owing to an increased chiasma frequency in oocytes in some of the pairing segments. Not surprisingly, the segregation products seen in metaphase II cells showed some differences from the pattern recorded in male germ cells. For T(2;4)1Go, the sex-related difference in segregation patterns resulted in a diminished expectation of genetically imbalanced gametes, although this was not the case for T(7;16)67H.

Crossing over analysis at pachytene in man.

The distribution of anti-MLH1 (MutL homologue 1) antibody labelling was studied in human prophase meiocytes. A labelling pattern consisting of distinct foci, always associated with the synaptonemal complex (SC) and never in closely juxtaposed pairs, was observed. Comparison of the number and general positions of autosomal foci with previous studies of the number and positions of autosomal chiasmata indicates that the anti-MLH1 antibody marks sites of crossing over in human pachytene spermatocytes. A mean number of 50.9 autosomal foci was observed from 46 human pachytene spermatocytes corresponding to a genetic length of 2545 cm. Division of these spermatocytes into sub-stages revealed that the number of foci remains stable throughout pachytene. A focus was found on the XY bivalent in 56.5% of the nuclei. The presence or absence of foci from the XY bivalent could not be correlated to pachytene sub-stage.

Chiasma frequency, distribution and interference maps of mouse autosomes

Chiasma frequencies were analysed and chiasma positions measured in diakinesis/metaphase I autosomal bivalents from oocytes and spermatocytes of F1 hybrid C3H/HeHx101/H mice. Twenty chromosome size ranks, including the presumptive X bivalent, could be distinguished in oocytes, and nineteen autosomal ranks plus the XY pair spermatocytes. Overall, mean cell chiasma frequencies of the two sexes did not differ significantly once the contribution of the presumptive X bivalent and the XY pair were taken into account. Sex related differences in chiasma distribution patterns were evident, however. In monochiasmate bivalents, the chiasma was most commonly located interstitially in oocytes while in spermatocytes it could be either interstitial or distal. In dichiasmate bivalents, the chiasmata tended to be more centrally located in oocytes than in spermatocytes. Minimum inter-chiasma distances did not appear to show any great variation in chromosome pairs of different sizes, however, mean inter-chiasma distances did increase with the bivalent length. The minimum-inter chiasma distance data suggest that chiasma interference is complete over a chromosomal segment equating to approximately 60Mb. Measurement of the positions of chiasmata along chromosome arms open up the possibility of producing chiasma-based genetic maps for all the autosomes of the mouse.

Non-random patterns of non-disjunctional orientation in trivalents of multiple Robertsonian heterozygotes of Dichroplus pratensis (Acrididae)

Metaphase I orientation of centric fusion trivalents was studied in 24 single, 19 double and 3 triple heterozygotes of Dichroplus pratensis. Different populations of this South American melanopline grasshopper are polymorphic for seven Robertsonian fusions, and the polymorphisms seem to be stable. Several cytogenetic factors involved in the orientation and segregation of the meiotic configurations such as chromosomal length, symmetry and number and position of chiasmata, have been analysed in previous works. In this paper we study another factor that is relevant in the above respect in individuals with more than one heterozygous fusion: interaction among configurations regarding orientation. Our results indicate that, when there are two or three trivalents present in the MI cell, there is an interaction in such a way that the number of metaphases in which the two or three trivalents are non-disjunctionally oriented is always significantly higher than expected under a hypothesis of independence. However, the number of cells in which all trivalents are disjunctionally oriented does not decrease significantly, so an increase of unbalanced gametes due to this factor is not expected. The stability of the polymorphisms would thus not be affected.

A new index for estimating genetic recombination from chiasma distribution data

Chiasma frequency and position are good estimators of genetic recombination in a population. Darlington proposed a recombination index that consisted of the sum of the haploid number (n) and the average chiasma number per nucleus (x); this index (n+x) represents the average number of elements that segregate independently, so that the number of possible gametes equals 2(n+x). Here a more accurate approach is intended by proposing an index that takes into account: (a) the proportional length of chromosomes and (b) the accurate position of chiasmata. The development of simulation programs and the study of real cases (v.gr. Leptysma argentina) demonstrated that the index of Darlington (a special case of Ir and I′r) is always an overestimation of the recombination level of a population. Hence indexes Ir and I′r are proposed for organisms that allow a reasonably accurate measurement of chiasma distribution.

Effects of constitutive heterochromatin and genotype on frequency and distribution of chiasmata in the seven individual rye bivalents

Number and distribution of chiasmata were studied in the single pair of homologous rye chromosomes in 29 chromosomal F1 hybrids between the seven disomic wheat rye addition lines of 'Chinese Spring'/ 'Imperial' and five selected inbred genotypes of cultivated rye by using the differential Giemsa staining technique. The results indicate that the number and position of chiasmata is independent from the amount and position of C-heterochromatin. Genotype had an effect on chiasma number, whereas chiasma distribution within bivalents appeared to be determined by morphological features of chromosomes. Late replicating DNA in constitutive heterochromatin may delay the separation of half bivalents if chiasmata are formed between them and the centromere.

Analysis of interference in a double interchange heterozygote of wheat (Triticum aestivum L.)

A cytological analysis of meiotic configurations in a double interchange heterozygote in common wheat, Triticum aestivum L., involving 3DL/4DS and 1AL/UN (unidentified) chromosomes is presented, where pollen mother cells were stained with Giemsa. The translocations were identified by C-banding and this staining procedure located the positions of chiasmata in meiotic configurations in both translocation complexes. A strong interference was found between the presence of chiasmata in the interstitial and neighbouring translocated segments. If a chiasma is present in the former, it excludes the simultaneous presence of one in the latter and vice versa. It was also observed that the simultaneous presence of chiasmata in both distal segments of a translocation quadrivalent is more frequent than other situations.

Spermatogenic delay and increased chiasma frequency in T70H/+ male mice with hydroxyurea-Trenimon limited spermatocyte populations.

T(1;13)70H/+ male mice were treated with hydroxyurea (HU) and Trenimon (T). This karyotype offers excellent possibilities for estimating number and position of chiasmata and segregation in meiotic anaphase I. By their cell-killing action during spermatogenesis, HU and T produce large gaps in the spermatogenic line. The surviving population between the gaps was analysed at diakinesis--metaphase I and metaphase II. We found by autoradiography a considerable retardation of the development from resting primary spermatocytes (RPS) to metaphase I and II as compared to untreated T70H/+ males. Furthermore we found increased chiasma frequencies in diakinesis--metaphase I (MI) and reduced nondisjunction frequencies at anaphse I as a result of the treatments applied. The latter effect could not be explained by the increased chiasma frequency.

Chiasma distribution in rye chromosomes of diploid rye and in wheat/rye addition lines in relation to C-heterochromatin

In five genetically different inbred lines of rye and in the seven 'Chinese Spring'/'Imperial' wheatrye addition lines, chiasma distribution in rye chromosomes was studied with respect to the amount and position of constitutive heterochromatin (Giemsa C-bands). In all inbred lines, rye chromosomes with one primary terminal band were more frequently found as univalents than those with primary bands on both telomeres. These chromosomes were most probably 5R and/or 6R. In the addition lines a highly significant reduction in the number of arms bound by chiasmata was found for rye chromosomes 5R and 6R. Because of the similar chiasma distribution in the inbred lines and in the rye chromosomes of the addition lines, no effect of the wheat genome on the number of chiasmata in the rye chromosomes can be ascertained. However, a relationship between chiasma frequency and chromosome arm length seems to exist, since under reduced chiasma conditions the two shortest arms of the rye complement, those of chromosomes 5R and 6R, frequently fail to form a chiasma. No effect of the large blocks of constitutive heterochromatin in the telomeres of the rye chromosomes on the position of chiasmata within a bivalent could be established.

Heterosis for chiasma frequency and quantitative traits in common beans (Phaseolus vulgaris L.)

Ten genotypes, including inbreds, hybrids, and advanced populations, were examined in order to elucidate the relationship between position and frequency distribution of chiasmata and quantitative traits, including yield heterosis in common beans. The hybrid and advanced population groups were determined to possess 83% and 54% increased chiasma frequency, respectively in contrast to inbred lines. The increase in chiasma frequency of these populations was further manifested in a high number of interstitial chiasmata. The regular and superior chromosome behaviour of the hybrids was found to be positively associated with quantitative measures on bean yield, harvest index and bean yield efficiency. The results were discussed from the point of view that: a) increased interstitial chiasmata may provide an effective mechanism for maintaining genetic diversity and heterosis in hybrid populations; and b) heterosis for chiasma frequency and quantitative traits may be due to dispersed genes on the chromosomes having combined intra-and interallelic interactions. The data provide evidence for the existence of positive associations between interstitially localized chiasmata with its recombination potential and regular chromosome behaviour to bean yield heterosis. The role of enhanced interstitial chiasmata to promote higher levels of genetic variation and heterozygous advantage is discussed.

Position and Frequency Distribution of Chiasmata inCepaea Nemoralis(L.)

SUMMARYPosition and frequency distribution of chiasmata on the single A group bivalent of Cepaea nemoralis has been studied in snails sampled from ten populations. Results indicate that there is no localisation of chiasmata between chromosome arms. In the majority of snails the distribution of chiasmata between cells is non-random although within cells normal interference relationships appear to operate along the A group bivalent.