Pachytene Pairing Research Articles

Chromosome‐specific desynapsis in the n = 2 race of Haplopappus gracilis (Compositae)

During cytological screening for pollen sterility in a wild population of Haplopappus gracilis (n = 2), several partially sterile plants were found that had good pachytene pairing but varying numbers of univalents. Some plants had chromosome A bivalents or A univalents, while in the same cells chromosome B had only bivalents. In other plants the reverse condition occurred; the B chromosome had B bivalents or B univalents and only A bivalents. This demonstrates a chromosome-specific effect for the desynapsis genes. Hybridization between the two homozygous mutant genotypes produced only normal bivalents; this indicates the two mutants are not alleles and each is recessive. An F2 generation showed independent assortment of the desynaptic mutations. The chromosome A bivalent is the larger of the two and normally has one or two chiasmata; the B bivalent normally has a single chiasma. Chiasmata distribution was tested in the desynaptic mutant A bivalents and showed an acceptable fit to a binomial distribution. This occurs also in heterozygous, asynaptic pairing control gene mutations. Analysis of the NOR bivalent in two hologenomic desynaptic mutations in tomato also showed a good fit to a binomial distribution of chiasmata. This indicates the same methods are applicable to diverse species.

The pattern of zygotene and pachytene pairing in allotetraploid Aegilops species sharing the U genome

Allotetraploid Aegilops species sharing the U genome, Ae. columnaris (UUMM), Ae. ovata (UUMM), Ae. triaristata (UUMM), Ae. triuncialis (UUCC) and Ae. variabilis (UUSS), regularly form bivalents at metaphase I of meiosis. The pattern of zygotene and pachytene pairing was analyzed by whole-mount surface-spreading of synaptonemal complexes under the electron microscope. The data indicated that at the zygotene stage the chromosomes were almost exclusively associated as bivalents; only a few multivalents (7%) were observed. These observations are discussed in relation to mechanisms of diploidization of polyploid meiosis.

A study of meiotic pairing, nondisjunction and germ cell death in laboratory mice carrying Robertsonian translocations

Frequencies of anaphase I nondisjunction, germ cell death and pairing abnormalities at pachytene were assessed in male mice singly heterozygous and homozygous for the Robertsonian (Rb) translocations: Rb (1.3)1Bnr, Rb(11.13)4Bnr and Rb(10.11)8Bnr. Rb homozygotes showed low frequencies of nondisjunction but substantial germ cell death. This germ cell death could not be attributed to problems at pachytene as Rb homozygotes showed no increase in pairing abnormalities over the (C3H/HeH x 101/H)F1 controls. Instead genic factors are involved. Rb heterozygotes showed substantial frequencies of nondisjunction and even greater germ cell death than found in the homozygotes. Pachytene pairing abnormalities were observed and it appears that these, together with genic factors, cause physiological perturbation of meiocytes, thereby promoting germ cell death, with nondisjunction of the trivalent as a sublethal response.

The effect of colchicine on meiosis in the Rhoeo discolor stabile complex translocation heterozygote

Rhoeo discolor (2n = 12) was used to study the effect of colchicine on chromosome pairing during meiosis. Pachytene pairing appeared unaffected, but only 17.5% of the PMCs formed a ring of 12 chromosomes at metaphase I of meiosis. While 27.5% of cells had a complete chain of 12, 49.0% had chain configurations of varying (2–11) number of chromosomes and 6.0% had complete univalence. Adjacent orientation was found in the majority of cells with chain complexes of 2–11 chromosomes. The result was highly disturbed anaphase I where 58.4% PMCs were abnormal. It is concluded that the presence of aberrant cells at metaphase I is either due to colchicine-induced ineffectiveness of pairing at the very small pairing regions or failure of chiasma formation.Key words: colchicine, meiosis, Rhoeo discolor, translocation heterozygote, univalents, alternate/adjacent orientation.

Genetic characteristics of spermatogenesis in the turkish hamster ( mesocricetus brandti) subjected to reduced temperature or light

1. 1.|A genetic study of Turkish hamster ( Mesocricetus brandti) spermatogenesis exposed to reduced temperature and/or light was made of pachytene pairing, crossing-over and disjunction during testicular regression and recrudescence. 2. 2.|Abnormalities were found in all three mechanisms in all experimental groups particularly in cold exposed testes during recrudescence.

C-bands and chiasma distribution in Scilla siberica (Hyacinthaceae)

The distribution of chiasmata and their relationship to heterochromatic segments in Scilla siberica (Hyacinthaceae) have been analyzed in pollen mother cell meiosis by means of a Giemsa C-banding technique. All chromosomes could be identified in the meiotic cells. C-bands have a clear effect on chiasma distribution. Regions adjacent to intercalary homomorphic C-bands showed higher chiasma frequencies than other euchromatic regions. Chiasma distribution in bivalents of chromosome variants without these intercalary C-bands is different from those with C-bands. Strongly heterozygous C-blocks lead to a pronounced reduction of chiasma frequency in their vicinity. Mechanical clues for this are found in pachytene pairing behaviour of heterozygous C-bands, which also indicates that euchromatin is constant and C-bands are variable and additional segments. Within one anther, equational separations of C-band heteromorphisms were less than expected from corresponding metaphase I bonds, presumably because of a lower chiasma frequency in early meiotic cells. Heteromorphic intercalary C-bands show that chiasmata do not terminalize. Only at the onset of anaphase I does chiasma resolution result in transitory configurations reminiscent of terminalization.Key words: Scilla siberica, C-bands, meiotic recombination.

Meiotic Regularization, Restoration of Seed Fertility and Alkaloid Content in the Induced Autotetraploids of Hyoscyamus albus L.*

AbstractColchicine‐induced autotetraploids produced in the medicinally important solanaceous plant Hyoscyamus albus (2n = 68) revealed a general increase in pollen, stomata and seed size, but resulted in the reduction of leaf size and plant height. Also, an initial performance trial showed a decline in biomass yield but an increase in alkaloid content of 16.2 %. Thus, in terms of alkaloid yield, the tetraploids demonstrated a slight improvement over diploids for this economic product.Seed fertility of the raw colchiploids was low but a higher value (> 80 %) could be obtained in advanced generations following rigid selection. High fertility was accompanied by a diploidized meiotic chromosome behaviour in the autotetraploids, with high bivalent pairing and regular anaphase separation. Bivalents were predominantly of open type in the autotetraploids as against a predominance of ring bivalents with distal chiasma localization in the parental diploids. The algebraic estimate of multivalent pairing frequency recorded even in the raw colchiploids was quite low (0.239) compared to that expected on the basis of random pairing (0.667), which further dropped to 0.107 in the C3 generation. Such reduction in multivalent frequency in autotetraploids could be brought about by a combination of reduction in crossover frequency and correction in pachytene pairing.

Pachytene pairing and oocyte numbers in mice with two single Robertsonian translocations and the male-sterile compound with monobrachial homology

Oocyte numbers and synaptonemal complexes were studied in two Robertsonian translocations, Rb(6.15)1Ald and Rb(4.6)2Bnr, and their male-sterile compound. Oocyte numbers in the compound were lower than those of either parent, and there was a marked difference between reciprocal crosses. Synaptonemal complexes of homozygous females appeared as 19 bivalents, those of single heterozygotes as 18 bivalents and a trivalent, and those of compound heterozygotes as 17 bivalents and a quadrivalent. Most trivalents were fully paired, whereas the majority of quadrivalents exhibited terminal asynapsis. About one-half of all oocytes had other pairing abnormalities, probably reflecting reduced survivability. Whereas all fully paired quadrivalents were present in cells not showing any pairing anomalies, one-half of the quadrivalents with terminal asynapsis were seen in oocytes with other anomalies. It is suggested that in oocytes destined for atresia, there is a predisposition to synaptic failure of translocation configurations. Additional oocytes are likely to break down because of the deleterious effect of the compound translocation on gametogenesis. This effect seems to be more pronounced in Rb1Ald/Rb2Bnr spermatocytes than in oocytes.

Pachytene pairing and sperm counts in mice with single Robertsonian translocations and monobrachial compounds

Data on testis weights, sperm counts, and synaptonemal complexes are presented for mice carrying the following Robertsonian translocations: Rb(6.15)lAld; Rb(4.6)2Bnr; Rb(4.15)4Rma; Rb(6.15)lAld/Rb(4.6))2Bnr, which is male-sterile; and Rb(6.15)lAld/Rb(4.15)4Rma, which is male-fertile. In RblAld/Rb2Bnr sperm were absent or sparse, whereas the sperm count in RblAld/Rb4Rma was just over 50% of the parental value. The translocated chromosomes appeared as fully paired bivalents in homozygotes, as trivalents in single heterozygotes, and as quadrivalents in compounds. About 20-40% of trivalents had unsynapsed ends. The proportion of quadrivalents with unsynapsed ends was about 85% in the male-sterile compound, compared with 75% in the male-fertile compound. The proportion of quadrivalents associated with XY was about 70% in both. Testis weights, but not sperm counts, were found to differ in two of three reciprocal crosses. It is concluded that, in addition to pairing failure and autosome/XY association, the effect of translocations on spermatogenesis is affected by other factors, including genetic background, inbreeding, and perhaps environmental factors. It remains to be elucidated whether pairing failure and XY association are primary or secondary effects.

Pachytene pairing in relation to sperm and oocyte numbers in a male-fertile reciprocal translocation in the mouse.

In adult males carrying the male-fertile reciprocal translocation T(2;4)13H, body weights, testis weights, and sperm counts were higher in heterozygotes than in homozygotes. Heterozygotes whose mothers were C3H/He exceeded their reciprocal counterparts in the same criteria. At 3-4 days of age, no significant differences between homozygous and heterozygous females were found in body weight, ovarian volume, or oocyte numbers, although mean oocyte volumes were somewhat larger in heterozygotes than in homozygotes. In homozygous males and females the synaptonemal complexes of rearranged chromosomes appeared as bivalents that were indistinguishable from normal bivalents. In most gametocytes of heterozygotes, the translocation was present in the form of a quadrivalent. The degree of pairing failure was greater in oocytes than in spermatocytes. Terminal asynapsis of quadrivalents was very rare in spermatocytes, but it affected one quarter of the oocytes. Only very few translocation configurations were associated with the XY bivalent. It is concluded that the number of sperm produced in male heterozygotes can match the general increase in vigor by the formation of a high level of fully paired quadrivalents, whereas a greater degree of terminal asynapsis in the quadrivalents of oocytes may indicate a slightly more deleterious effect of this translocation on oogenesis.

The effect of Ph gene alleles on synaptonemal complex formation in Triticum aestivum � T. kotschyi hybrids

Chromosome pairing at zygotene-pachytene was studied in Triticum aestivum × T. kotschyi hybrids (2n=5x=35, genomic constitution ABDC(U)S(v)) by electron microscopy of synaptonemal complexes in spread microsporocyte nuclei. Hybrids carrying either the Ph allele or the ph allele, which differ markedly in metaphase I pairing, are both capable of greater than 90% pachytene pairing, although pairing in the Ph hybrids appeared slower or less synchronised. In both genotypes branched synaptonemal complexes were formed by intra-and interchromosomal pairing. The Ph gene control on homoeologous pairing does not act on the ability to pair into synaptonemal complexes. It may act on the rate of pairing or the time of crossing over.

EM investigations of surface spread synaptonemal complexes in a human male carrier of a pericentric inversion inv(13)(p12q14): the role of heterosynapsis for spermatocyte survival.

EM investigations of surface spread synaptonemal complexes of pachytene spermatocytes were performed on a human male carrier of a pericentric inv(13), ascertained through his daughter with a duplication-deficiency of the same chromosome. The inv(13) bivalent could be unambiguously identified by either its asymmetrical kinetochores or its nucleolar association or both. There was scarcity of reversed homosynapsis of the inverted segments with inversion loops, possibly related to the small size of the inversion. The majority of pachytene spermatocytes showed the inverted segment to be either asynapsed or heterosynapsed. Generally initial homosynapsis is highly efficient with high fidelity, while heterosynapsis at the secondary pachytene pairing phase may take place with any available partner remaining unsynapsed and including the differential segments of the XY. It is suggested that survival of spermatocytes to later stages of meiosis may be ensured by heterosynapsis, and the recombinant chromosome in the offspring might be the result of a U-type exchange.

Synaptic adjustment, non-homologous pairing, and non-pairing of homologous segments in sex chromosome mutants of Ephestia kuehniella (Insecta, Lepidoptera)

Microspread pachytene nuclei of wild-type and W chromosome mutants of the mealmoth Ephestia kuehniella were used to study synaptonemal complex (SC) formation. In structurally heterozygous bivalents, axial elements of considerable length differences were brought to the same length by synaptic adjustment. The adjustment length was a compromise between the mutant and the wildtype homologue length in a structural heterozygote of a W chromosome-autosome translocation, T(A; W). The translocated non-homologous W segment really participated in SC formation as could be seen from the W chromosomal heterochromatin, used as a cytogenetic marker. Pachytene pairing of the wild-type W-Z bivalent extended from about two-thirds to the full length of the W chromosome, though from cytogenetic and genetic evidence W and Z are largely — if not completely — non-homologous. Nonhomologous pairing was even more conspicuous in sex chromosome bivalents containing a deleted W chromosome, Df(W). In one of the pairing configurations the halves of the Z chromosome were synapsed to either side of the Df(W). Thus, one side was pairing with the Df(W) in reversed order. The pairing behavior of the W with homologous chromosome segments was tested by introducing supernumerary W segments via the T(A; W) translocation. Pairing between the W and the translocated homologous W segment never occurred, whereas the Z frequently synapsed with it. Even in T(A; W) homozygotes, pairing between the two translocated W segments was not regularly found while the autosomal parts of the translocation chromosomes were always completely paired. Homologous chromosomes and the ability to form an SC are not sufficient for pairing initiation. Specific loci or sequences are postulated for this function. They are either absent from the W chromosome or are present in only low concentrations.

Male pachytene pairing in single and double translocation heterozygotes and spermatogenic impairment in the mouse.

In order to clarify the relationship between meiotic pairing and progress of spermatogenesis, an analysis of male meiotic pairing was carried out in four reciprocal translocation heterozygotes and two double heterozygotes for two semi-identical reciprocal translocations. The reciprocal translocations were chosen to range from fertility (T70H/+) through almost complete sterility (T31H/+) to complete sterility (T32H/+, T42/H+). If meiotic pairing in the translocation multivalent was incomplete, it concerned terminal or probably more often proximal chromosome segments (Chain IV). If both segments failed to pair the multivalent symbol is Chain III + I. Complete pairing is symbolized by Ring IV. To contrast and complement observations of this type, the double heterozygotes were introduced. Males of this type in theory possess two heteromorphic bivalents with a central area of incomplete meiotic pairing (loop formation). Of the T70H/T1Wa double heterozygotes, 36% of the males are capable of inducing at least one decidual reaction in two females whereas for T26H/T2Wa, 79% of the males can do so. For the reciprocal translocations, it was found that proximity of the multivalent to the sex bivalent during pachytene increased in the order Ring IV, Chain IV, Chain III + I. The degree of spermatogenic impairment as measured from cell counts in histological sections and tubular whole mounts, is positively related to the frequency of proximity between the sex chromosomes and the translocation multivalent and thus to lack of meiotic pairing within the multivalent. The meiotic pairing analysis of the double heterozygotes yielded the following findings. For the long heteromorphic bivalents a true loop was never seen in T70H/T1Wa and only rarely observed in T26H/T2Wa. Small marker bivalents of both types were usually recognizable by the following criteria: pairing confined to distal or proximal segments, both distal and proximal segments pairing and loop formation and pairing covering the entire length of both "homologues" but the longer one often with a "thickened" lateral element. The same positive correlation between the absence of pairing (proximal, distal or central) and the proximity of the small marker bivalent synaptonemal complex to the sex bivalent has been found as for unpaired segments within reciprocal translocation multivalents. One unexpected finding was the occurrence of diploid spermatids and spermatozoa especially in T32H/+ males (70-91%) but also in T31H/+ (3-39%).

Pachytene analysis in six species of Eu-Sorghum and their hybrid.

Critical analysis of chromosomes at pachytene and later stages of microsporogenesis in six different species of Eu-Sorghum namely S. vulgare, S. durra, S, caudatum, S. roxburghii, S. sudanense and S. virgatum and their 15 F1 hybrids were made. The hybrids involving one wild and one cultivated species showed relatively higher proportion of chromosomal abnormalities than those involving either both cultivated or both wild species. Pachytene pairing was found to be complete and apparently normal in two S. sudanense×S. durra and S. caudatum×S. roxburghii hybrids. Pachytene analysis in remaining 13 hybrids revealed the presence of some minute, though cytologically detectable, structural differences such as terminal as well as interstitial non-paired regions, small duplications and terminal deletions, and differential segments between the parental species. In spite of the existence of these meiotic irregularities in some hybrids, the subsequent stages of meiosis were quite normal leading to good seed setting. Cytogenetical mechanisms underlying species differentiation in the genus are discussed.

Pachytene pairing in relation to pollen fertility in five cultivars of cassava.

Pachytene pairing in relation to pollen fertility was studied in five cultivars of cassava. The two highly pollen fertile clones showed only normal pachytene and later meiotic divisions were also normal. However, in the partially pollen fertile clones different pachytene abnormalities like non-pairing, deletion, duplication and inversion were found in different chromosomes. In C1-1443 as many as five bivalents showed aberrant pachytene pairing. Though there was a slight reduction in chiasma frequency, later divisions were normal. Based on the extent of pachytene abnormalities in different clones, reduction in chiasma frequency, meiotic sequence and normal tapetum development and microsporogenesis, it is concluded that pachytene behaviour had a statutory role in determining the ultimate pollen fertility in cassava.

Meiotic Behaviour of Spontaneous and Mutagen Induced Partial Desynaptic Plants in Pearl Millet

Partial desynaptic plants were isolated from normal population of pearl millet (Pennisetum typhoides S. and H.) inbred T55 and mutagen (EMS and gamma-rays) treated populations of inbreds Tif23A, Tif23B and K560. The pachytene pairing was complete and normal. A variable number (2-14) of univalents occurred at MI. Anaphase I separation was normal in the majority (66-79%) of the cells; many showed 8:6 and 9:5 chromosome separation. The spontaneous desynaptic plant showed laggards and chromatin bridges at anatelophase I, while the induced ones did not show these aberrations. Chiasma frequency in the desynaptic plants was lower than that in the normal controls.

PHENETIC ANALYSIS AND THE PHYLOGENY OF THE DIPLOID SPECIES OF GOSSYPIUM L. (MALVACEAE).

Studies of interspecific relationships, evolution, phylogeny, and the systematics of Gossypium are numerous. Phillips (1966) recently summarized the cytogenetic data upon which current views are based, and Fryxell (1969) presented a brief account of the systematics of the genus that is in accord with these data. Distributional maps are also available (Anonymous, 1968, Figs. 2, 3). Recent papers by Cherry et al. (1970) and by Johnson and Thein (1970) have utilized data on the electrophoretic analysis of seed proteins to assess species relationships in Gossypium and to draw phyletic conclusions. The two papers, although supporting one another in broad outline, do not agree in many specific details, and consequently reach certain different conclusions. For example, Johnson and Thein show G. armourianum and G. harknessii to have very similar patterns of protein bands, whereas Cherry et al. find them to be distinctly different. Conversely, the latter authors find G. anomalum and G. triphyllum similar, while the former authors find them to be different. In view of these discrepancies, it is difficult to assign significance to the seed protein data until the basis for these discrepancies can be clarified. Cytogenetic data can be uniquely valuable in providing evolutionary understanding, by demonstrating such things as aneuploid and polyploid series, and by tracing complex patterns of genome relationships among amphidiploids and their relatives. None of these phenomena occur, however, in the diploid species of Gossypium that are under consideration here. In Gossypium the cytogenetic data from which phylogenetic interpretations can be derived concern principally the degree of chromosome pairing in interspecific hybrids. Cytogenetic data have limitations. Certain hybrids have not been or cannot be produced, or are not viable even with such aids as embryo culture. Consequently, the data that can be applied to the question of species relationships have numerous omissions. Cytogenetic data, bearing on species relationships, may be gotten from: chromosome pairing behavior at meiotic metaphase I; chiasmata frequency at metaphase I; pachytene pairing behavior; or genetic segregation data in advanced hybrid generations. Data on pachytene pairing are not conveniently accessible in Gossypium. Genetic segregation data of diploid interspecific hybrids have been reported for only a few crosses (Saunders, 1961; Endrizzi and Brown, 1968), and in any case are only available for those species pairs that will produce fertile hybrids. Consequently, the available evidence is confined largely to data derived from studies of meiotic metaphase-specifically, measurements of univalent and bivalent frequencies and of chiasmata frequencies. These metrics are relatively insensitive measures of affinity. This insensitivity gives rise to the possibility of misleading conclusions about species relationships. Poisson et al. (1969) have noted other shortcomings of this kind of data in assessing species relationships in Gossypium. The assessment of evolutionary affinity from seed protein data is subject to several criticisms. The assumption that protein

PACHYTENE KARYOTYPES OF 2XHAPLOIDS DERIVED FROM TETRAPLOID ALFALFA (MEDICAGO SATIVA) — EVIDENCE FOR AUTOTETRAPLOIDY

Five 2x haploid plants derived from three different tetraploid Mediaago sativa L. plants all had normal pachytene pairing, and their karyotypes were very similar to that of diploid M. sativa. A hybrid of one 2x haploid with diploid M. falcata L. also had a normal karyotype. The pachytene chromosome lengths of the 2x haploids were shorter than those of diploid M. sativa and M. falcata but close to values for tetraploid M. sativa and autotetraploid M. falcata. The results presented support an autotetraploid origin of the parental tetraploid alfalfa.

Alfalfa Chromosomes. III. Medicago Glomerata Balb. Pachytene Karyotype1

The pachytene idiogram of Medicago glomerata Balb. was found to be almost identical to that published for M. sativa L., only two arm ratio means and two chromosome length means differing significantly between the two species. The M. glomerata idiogram was also similar to a M. falcata L. idiogram, although in this case there were greater differences. Hybrids between M. glomerata and both M. sativa and M. falcata had normal pachytene pairing. Hence M. glomerata may be a common ancestor of both M. sativa and M. falcata.