Frequency Of Chiasmata Research Articles

Meiotic behaviour in natural diploid, tetraploid, and commercial diploid crested wheatgrass

Chiasma frequencies and chromosome associations at diakinesis and first metaphase (MI) were studied in natural and commercial diploid Ag‐ropyron cristatum and natural tetraploid Agropyron desertorum crested wheatgrass plants. The frequencies of bivalents were 6.988 and 6.980 at diakinesis and 6.980 and 6.976 at MI in the natural and commercial diploids, respectively. The frequencies of bivalents and quadrivalents in the natural tetraploid were 7.728 and 3.072 at diakinesis, and their frequencies at MI were 7.880 and 2.984, respectively. A few univalents were formed at diakinesis and MI in the three crested wheatgrasses, and these were generally associated with trivalents at the two stages in the tetraploid. There were positive and significant correlations between the frequencies of chiasmata at diakinesis and those of chiasmata at MI in the three crested wheatgrasses. Tetraploid A. desertorum, in particular, is thought to be an important breeding material for future studies when growth performance and meiotic regularity are taken into consideration.

Plantago ovata: genetic diversity, cultivation, utilization and chemistry

Plantago ovatais the cultivated and economically important species in the monotypic genusPlantago. P. ovatais a short-stemmed annual herb, 10–45 cm tall. The species is generally an in-breeder. The seed husk of this plant is commonly called Psyllium or Isabgol (in Hindi), which is a very effective laxative. Other usages of Isabgol are in ice cream making, cosmetics, printing and finishing. The intake of husk also reduces blood cholesterol levels. Isabgol is commercially very important as its export earns India foreign exchange worth INR 2.5 billion (US$1=44 INR). The plant is cultivated on a large scale in western India. In Gujarat, it is cultivated in about 144,000 ha of land, yielding 720 kg/ha.P. ovatahas a narrow genetic base, and the lack of variability is on account of low chromosome number, small chromosome size, presence of high heterochromatin in the chromosomes, low chiasmata frequency and low recombination index. The genome size of the species is ∼500 Mb. Different breeding methods, namely selection, hybridization, induced mutations, polyploidy and tissue culture, have been used for genetic improvement of this plant. Except selections, which have led to isolation of a few varieties, the results of other methods have not been encouraging.P. ovatahas about 200 wild allies, some of which are medicinally important. These wild species constitute a rich resource of important genes, which if transferred to cultivated species could revolutionize the production of Isabgol. The present paper highlights various aspects of genetic diversity, cultivation and utilization of this important medicinal plant, and suggests the prospects of genetic manipulation.

From spermatocytes to sperm: meiotic behaviour of human male reciprocal translocations.

Human male translocation carriers may present alterations in the meiotic process due to the presence of the translocated chromosomes. The aim of this work was to study the mechanisms that affect meiotic segregation in translocation carriers by analysing different stages of the meiotic process. Meiotic studies using fluorescence in-situ hybridization on both spermatocytes and sperm nuclei were performed in two translocation carriers, t(11;17)(q13.1;p11.2) and t(10;14)(q24;q32). A ring configuration was the main type of quadrivalent found in metaphase I. Overall chiasma frequency was significantly decreased in the t(11;17) carrier. In the t(10;14) carrier, chiasma frequency within the interstitial region of chromosomes 10 and 14 was increased and the recombination pattern was modified. As expected from the frequencies of interstitial chiasmata found in metaphase I in the two subjects, the incidence of asymmetric dyads was sporadic in t(11;17) and very high in t(10;14). In both carriers, segregation frequencies observed at metaphase II were not different from the segregation data obtained in decondensed sperm nuclei. The concordance observed among results obtained in different spermatogenic stages indicates an absence of cellular selection based on chromosomal imbalances. Results obtained in the aneuploidy assay have not provided any evidence for an interchromosomal effect.

Chiasma Frequency in Frogs of the Genus Leiopelma (Amphibia; Anura) and a Test of the Hypothesis of Inducible Recombination

The rate of recombination in three species of Leiopelma (Leiopelmatidae, Anura) from New Zealand was estimated by measuring chiasma frequency in spermatocyte bivalents. Both the mean and intra-individual variance of excess chiasmata frequency differed among the three species (L. hochsletteri = 13.17 5 2.96 SD, L. harnilroni = 9.69 + 1.16 SD; L. archeyi = 10.71 1.1 1 SD). L. hochstetteri has one of the highest rates of intra-individual variation in chiasma frequency found in frogs. The presence of supernumerary chromosomes in L. hochsretteri was used to test the theory of inducible recombination. If supernumeraries are parasites, then they will be associated with an increase in either chiasma frequency or an increase in within-individual variance. However, this was not found in L. hochsferteri, Nevertheless, the high variance in chiasma frequency associated with these putative genomic parasites in L. hochstetteri makes it impossible to rule out the Red Queen hypothesis as an explanation.

Giemsa C-Banded Karyotypes of two Cytotypes (2x, 4x) of Psathyrostachys Lanuginosa (Poaceae; Triticeae)

The karyotypes of the diploid (2n = 2x = 14) and tetraploid (2n = 4x = 28) cytotypes of the outbreeding P. lanuginosa collected from one population in China were investigated by Giemsa C- and N-banding and AgNO3 staining. The complement of the diploid consisted of 14 large chromosomes: 8 metacentrics and 6 SAT-chromosomes, one metacentric and 2 submetacentric pairs, with small to minute, polymorphic, completely heterochromatic satellites. Except that only eight SAT-chromosomes were observed, the complement of the tetraploid matched a doubling of that of the diploid and indicated an autoploid origin. The existence of 12 chromosomes with nucleolus organizers was established through AgNO3 staining demonstrating nucleoli. C-banding patterns comprised from zero to three (2x), or four (4x) small bands per chromosome giving a low content of constitutive heterochromatin (< 3 percnt;). The level of banding pattern polymorphism was low. N-banding produced no bands. Variation in the size of nucleoli demonstrated a differential nucleolus forming capacity of nucleolus organizers among SAT-chromosomes. The basic karyotype was similar to those of P. fragilis, P. juncea and P. stoloniformis, indicating a close relationship and the presence of genome N. Meiotic analysis suggested the presence of a chromosomal rearrangement in the diploid. The frequency of interstitial chiasmata was high. Differences in pollen diameters differentiated the two cytotypes.

Chiasma Frequency and Distribution in Males and Females of Metaleptea Bremcomis Adspersa (Acridinae, Acrididae) with and without B. Chromosomes

Previous studies on the South American grasshopper Metaleptea brevicomis adspersa revealed the existence of a widespread polymorphism for a large B chromosome with isochromosome characteristics. In this work, we analyse the frequency and distribution of chiasmata in OB and IB males and females belonging to two populations in Misiones province (Argentina), from the localities of Wanda and Eldorado. The comparative analysis of meiosis in both sexes revealed significant differences between OB males and females, the latter having significantly lower chiasma frequencies. Chiasma distribution is also significantly different. M. b. adspersa is thus a new example of “two-track heredity” where the homogametic and not the heterogametic sex is the one that shows limited recombination. The B chromosome present in both populations tends to increase chiasma frequency slightly in both sexes.

Male and Female Meiosis in Nicotiana tabacum L.

Male and female meiosis has been studied together for the first time in Nicotiana tabacum (2n=48) collected from 2 populations. Meiotic studies revealed differences in the behavior of chromosomes in the 2 sex cells i.e. pollen mother cells (PMCs) and embryo sac mother cells (EMCs) particularly with respect to frequency of chiasmata. Male sex cells (PMCs) showed a higher chiasmata frequency than female sex cells (EMCs) which show 14.33 and 11.48% reduction in chiasmata frequency in the 2 populations. The practical importance of female meiotic studies is discussed.

Lampbrush chromosomes in the japanese quail Coturnix coturnix japonica: cytological maps of macro chromosomes and meiotic crossover frequency in females

Cytological maps of lampbrush macrobivalents of the Japanese quail (Coturnix coturnix japonica) were constructed. Investigation of chiasmata allowed determination of the meiotic frequency of reciprocal genetic recombination (crossing over) in Japanese quail females. The total chiasma number in bivalents of Japanese quail oocyte nuclei was determined to be 53-58. Macrobivalents 1-5 and Z of the Japanese quail had on average 3.3 chiasmata per bivalent, and microbivalents, 1.0-1.1 chiasmata per bivalent. The chiasmata (crossover) frequency in Japanese quail females was lower than in chicks. In macrochromosomes of Japanese quail females, one crossover occurred per 43.9 Mb, and in chicken, per 30.0 Mb. Judging from chiasma frequency, the genetic length of the Japanese quail genome is likely to be 2650-2900 cM. Crossover frequency in the species was 0.023 per Mb in macrobivalents and 0.07-0.08 Mb in microbivalents and for the total genome, 0.041 crossovers per Mb. The genetic length of one Mb (theta) in female Japanese quails was 1.14 cM in macrochromosomes, 3.60-4.12 cM in microchromosomes, and about 1.96-2.15 cM averaged over the genome.

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.

Evolutionary Trend in Lens culinaris and Allied Spcies. A Cytological Evidence.

The karyotype of 20 cultivated varieties of lentil and 3 wild species revealed a good deal of structural variations. The chromosomal length ranged from 4.58 to 7.50 μm in L. orientalis, 3.86 to 6.11 μm in L. nigricans and 3.81 to 8.37 μm in L. montbrettii. The karyotype of L. montbrettii was assymetrical. Secondary constriction was noticed in the longest chromosome of the L. montbrettii and L. orientalis whereas it was present on the 3rd pair in L. nigricans. Total chromatin length. was 44.5 μm in L. orientalis, 34.64 μm in L. nigricans and 39.64 μm in L. montbrettii. Out of 20 genetic stocks of lentil most possessed 4-7 chromosomes with submedian centromere. In some varieties like L 3991, 74 TA 9/ILL 15 and LC 112, 3 to 4 pairs of chromosomes possessed median centromere. The size difference between the shortest and the longest chromosomes in most of the strains was less than 2 μm. Among different varieties “J” shape submetacentric chromosomes outnumbered the “V” shape metacentric chromosomes. Submetacentric chromosomes approaching acrocentric condition was found in few varieties like WYR 1811, 74 TA 276/ILL 262, 75 KT 36261/ILL 553 and Pant L 639. Most of the exotic lentil accessions possessed 0-1 metacentric and 6-7 submetacentric chromosomes and indigenous lines possessed 2-5 submetacentric and 2-4 metacentric chromosomes. Most of the karyotypes are symmetrical but a tendency towards evolution of asymmetrical is very much apparent within the species as also revealed by T. F. Meiosis in the majority of the cultivars under study showed near normal chromosomal pairing, except infrequent occurrence of univalents and multivalents. The average chiasmata frequency per bivalent was found to range from 0.8 to 1.8 in different cultivars. The exotic macrosperma cultivars in general possessed lesser chiasmata per bivalent indicating them as genetically advanced. The number of rod bivalents outnumbered the ring bivalents in all the wild species.

Differences in the synaptic pattern in two autotetraploid cultivars of rye with different quadrivalent frequencies at metaphase I

Synaptic behaviour of the two tetraploids rye cultivars Gigantón (G) and Tetrapico (T) displaying significant differences in their quadrivalent frequencies at metaphase I was analyzed by electron microscopy in surface-spread prophase I nuclei. A different behaviour was observed between the two cultivars; the synaptonemal complex (SC) quadrivalents frequency being significantly higher in G than in T at prophase I. Moreover, the G SC quadrivalents had more synaptic partner exchanges (SPEs) and their location was more distal than the T SC quadrivalents. However, inverse findings were found at metaphase I, the quadrivalent frequency was higher in T than in G. The role that different factors, mainly the number and location of the SPEs and the frequency and distribution of chiasmata, could play in the evolution from prophase I to metaphase I in both cultivars is discussed.Key words: autotetraploid rye, synaptonemal complex, spreading.

Development of high-gossypol cotton plants with low-gossypol seeds using trispecies bridge crosses and in vitro culture of seed embryos

The objective of this work is to develop an upland cotton, Gossypium hirsutum L. [2n = 4x =52, 2(AD)h], having a reduced level of gossypol in the seeds for food and feed uses, and a high level of gossypol in the remaining organs to limit pest incidence. Using G. sturtianum Willis (2n = 2x = 26, 2C1) as donor and G. thurberi Torado (2n = 2x = 26, 2D1) or G. raimondii Ulbrich (2n = 2x = 26, 2D5) as bridge species, two trispecies hybrids G. thurberi– G. sturtianum– G. hirsutum and G. hirsutum– G. raimondii– G. sturtianum were synthesized. Both trispecies hybrids were male sterile. Recurrent backcrossing to G. hirsutum as pollinator and selfing of the second backcross (BC) progenies resulted in seeds which were rescued by in vitro culture. In total, 1208 flowers of the trispecies hybrids and their BC progenies yielded 192 seed embryos from which 62 plants were obtained. Cytogenetic analyses indicated a relatively high frequency of chromosome pairing and chiasmata. The gland levels in backcross seeds ranged from glandless seeds to normally glanded seeds. All vegetative parts of those hybrids were glanded, but a wide range of variability for gland density was observed on leaf, stem, bract and calyx. Plants derived from seeds having a reduced level of gossypol constitute very interesting germplasm to develop a cultivated glanded cotton with low-gossypol seeds.

Karyotype, DNA Content and Meiotic Behaviour in Five South American Species ofVicia(Fabaceae)

This paper presents the karyotype, DNA content and meiotic behaviour of five species ofViciafrom Argentina (V. macrogramineaBurk.,V. gramineaSM.,V. epetiolarisBurk.,V. pampicolaBurk. andV. nanaVog.). All the species have the same chromosome number and karyotype formula (2n=14; 6m+4st+4t). 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 inV. nana(annual) and higher inV. 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 ofV. gramineaand that of the other species.V. gramineahas 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.

Cytogenetic Investigation of Setaria verticillata L. and Eragrostis aegyptiaca Willd. from Egypt.

Two species of Setaria verticillata and Eragrostis aegyptica from Egypt were carried out under cytogenetic investigation in this study. They are very common and widely spreed grass belong family poaceae, mostly distributed in Nile delta region.All accessions collected for each species show no significance variation in morphological measurements. Mitotic chromosome investigation shows that Setaria verticillata has 18 chromosomes (x = 9) as diploid species, where Eragrostis aegyptiaca has 40 chromosomes based on x =10 as tetroploid species. Karyotype structure of the two species shows degree of dissimilarity of the first species within chromosome set in the length and centromere position (show types of metacentric, submetacentric and telocentric). Chromosome set also shows satellite chromosome with probability of translocation in one pair of chromosomes. In contrast the second species shows a karyotype structure with high degree of homogeneity in length and centromere position (mostly metacentric).Parameters of meiotic division as chromosome association, chiasmata frequency and pollen fertility as well as seed set were investigated for the two species. Meiosis of Setaria verticillata recorded low chiasmata frequency, low pollen fertility low percentage of seed set and more frequent aberrated cells. This in contrast to Eragrostis aegyptiaca, where meiosis show, normal behaviour of chromosomes, low aberration, high fertility and seed set.The mitotic and meiotic results observe the cytogenetic situation of the two species. The results pointed to the genetic instability of Setaria verticillata and the probability of hybriditynature of the species through out breeding with near by another diploid species. On other hand the results insure the genetic stability of Eragrostis aegyptiaca and confirm its autotetraploid nature.

Chromosome association and pollen fertility of parental and interspecific hybrids of Lycopersicon esculentum X L. hirsutum and L. pennellii

Cytological studies were carried out on two wild species (L. hirsutum and L. pennellii) and the cultivated species (L. esculentum) of tomato and their F1 hybrids. Both parents and hybrids show a diploid chromosome number of 2n=24. The meiotic behaviour of the cultivated species showed a high degree of chromosome homology resulting in a high level of chiasmata frequency per bivalent. In contrast, the two wild species showed a slight increase in uniyalent frequency and a decrease in bivalent formation and chiasmata frequency. The meiotic behaviour of the hybrids showed a high level of univalents and low levels of bivalents as well as trivalents. Highly significant decreases in chiasmata frequency and increases in meiotic abnormalities, especially in the L. esculentum X L. pennellii hybrid, also were detected. The high meiotic irregularity and low chiasmata frequency recorded in the second hybrid indicated the disharmony and difference between its parental genomes and also served to predict its sterility. With regard to degree of pairing recorded in the hybrids, there is a possibility that sterility in such cases may refer to genetic factors in addition to the previously mentioned reasons. Pollen fertility showed no great difference between L. esculentum and L. hirsutum and their F1 hybrid, but a significant decrease was recorded in the L. esculentum X L. pennellii hybrid, which was clearly associated with high meiotic irregularity, low chiasmata frequency and chromosome association.

Hybridization Studies on Blattella germanica and B. asahinai (Dictyoptera: Blattellidae): Chiasma Frequency and Distribution

Chiasma frequency and distribution were studied in Blattella asahinai Mizukubo and interspecific hybrid males from crosses of B. asahinai × B. germanica (L.). Observations were made on male meiocytes in late dialdnesis. Chiasmata were localized at or near the ends of the chromosomes in both species. Chiasma frequency was lower and less variable in B. asahinai than in B. germanica. In the interspecific hybrids, the frequency was closer to that of B. asahinai than B. germanica. Chiasmata in hybrids were redistributed into regions where chiasmata are rare in the parent species. Chiasma frequency and the range of variation in chiasma frequency and in the frequency of internal chiasmata were affected by the species of the maternal parent. The maternal influence may be the result of a nonreciprocal translocation that involves the X chromosome and that separates the two species.

A genetic map of DNA loci on bovine chromosome 1

We constructed a genetic map of most of the length of bovine chromosome 1 using the CSIRO and the Texas A&M University cattle reference families. Twelve loci are in a single linkage group, 9 of which are highly polymorphic loci. Four loci are of known biochemical function, α-1 crystallin (CRYA1), γ-s crystallin (CRYGS), superoxide dismutase 1 (SOD1), and uridine monophosphate synthase (LIMPS), and these have also been previously mapped in humans. The loci CRYA 1, CSRD 1613, GMBT 7, RM 95, SOD I, and LIMPS had been previously assigned to bovine syntenic group U10, while CSRD 1613 and LIMPS had also been assigned to chromosome 1 by in situ hybridization. All of the loci show statistically significant linkage to at least one other locus. The conserved loci indicate that there have been major rearrangements during the evolution of bovine chromosome 1 compared to other mammalian chromosomes. The estimate of the total length of the linkage group is 168 cM, which accords well with the predicted length based on chiasmata frequencies for the bovine genome and the relative size of chromosome 1 in the bovine genome.

Chiasma distribution in the first bivalent of mice carrying a double insertion of homogeneously-staining regions in homo- and heterozygous states.

An examination of the meiotic pattern of chromosome 1 isolated from a feral mouse population and containing a double insertion (Is) of homogeneously-staining regions (HSRs) was carried out. In a previous study is was shown that the region delineated by the proximal breakpoint of Is(HSR;1C5) 1Icg and the distal one of Is(HSR;1D)2Icg is unpaired during early pachytene and heterosynapsed at midpachytene. No synaptic disturbances were revealed in homozygotes in this study. Chiasmata number per first bivalent in heterozygous (1.87) and homozygous (1.88) males was shown to be higher than in normal ones (1.61). In normal males a single chiasma is located in the medial part of chromosome 1. In heterozygotes this segment is heterosynapsed and unavailable for recombination. This leads to a significant decrease in the frequency of bivalents bearing a single chiasma and an increase in the frequency of bivalents bearing double chiasmata located mostly at subcentromeric and subtelomeric regions of the chromosome. In homozygous males the frequency of double chiasmata is also increased, and even triple chiasmata become possible because of the increase in the physical length of the bivalents. Thus insertion of heterochromatic regions, which are inert with respect to recombination, leads to an increase in the length of the genetic map of the chromosome because of relaxation of interference restrictions.

A NEW SPECIES IN SECTION ARACHIS OF PEANUTS WITH A D GENOME

Arachis glandulifera Stalker is a diploid (2n = 2x = 20) taxon in section Arachis native to eastern Bolivia. Plants of A. glandulifera have longer lateral branches than other taxa of section Arachis, an upright mainstem, prostrate lateral branches, and larger flowers and seeds than other wild species in the section. The pods are greatly reticulated. Glandular trichomes are present on vegetative plant parts and the peg. Intraspecific hybrids among four accessions are fertile and uniformly have ten bivalents in pollen mother cells. Three accessions had nearly identical karyotypes, while a fourth had subtelocentric chromosomes 6 and 9. Hybrids between A. glandulifera and two other diploid species of section Arachis were male‐sterile, and chiasmata frequencies ranged between 5.8 and 12.1 per cell. Attempts to hybridize the species with A. hypogaea failed. A new species description and D genomic classification are proposed for A. glandulifera, which is different from previously described A and B genomes of section Arachis.

Molecular organisation of the plant genome: Its relation to structure, recombination and evolution of chromosomes

Large scale changes in nuclear DNA amount accompany the evolution of species of higher plants. Much of the nuclear DNA accrued during the evolution of species does not encode genetic information and is selectively neutral. Nonetheless, the pattern of distribution of the excess DNA within and between chromosome complements suggests that there are rigid constraints underlying evolutionary changes in genome organisation. A five-fold increase in the amount of nuclear DNA has occurred in the evolution ofLathyrus species. Not withstanding this massive DNA variation, species show consistently similar patterns in base sequence proliferation, divergence and DNA distribution within and between chromosome complements. Within chromosome complements, the excess DNA is distributed evenly in all chromosomes irrespective of the large differences in chromosome size and, between complements, DNA distribution is discontinuous; species cluster into DNA groups with remarkably regular intervals. Similar constraints govern the frequency and distribution of chiasmata in the chromosome complements. Between species chiasma frequency and nuclear DNA amounts are not correlated but within complements it is positively correlated with the amount of DNA contained in each chromosome. It is shown that constraints upon evolutionary changes in genome organisation could restrict or predetermine the outcome in chromosome evolution.