Bivalents In Metaphase Research Articles

Microscopic Procedures for Plant Meiosis

Research Article| October 01 1997 Microscopic Procedures for Plant Meiosis James P. Braselton James P. Braselton Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (1997) 59 (8): 502–506. https://doi.org/10.2307/4450365 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation James P. Braselton; Microscopic Procedures for Plant Meiosis. The American Biology Teacher 1 October 1997; 59 (8): 502–506. doi: https://doi.org/10.2307/4450365 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Copyright 1997 The National Association of Biology Teachers Article PDF first page preview Close Modal You do not currently have access to this content.

Kinetic organization of metaphase I bivalents in spermatogenesis of Lepidoptera and Trichoptera species with small chromosome numbers

The fine structure of bivalents in metaphase I spermatocytes of two Lepidoptera species, Orgyia thyellina Butler (n = 11) and O. antiqua (L.) (n = 14) (Lymantriidae), and a Trichoptera species, Limnephilus decipiens (Kolenatý) (n = 10) (Limnephilidae) were studied using a series of ultrathin sections and transmission electron microscopy. The bulk of species in both orders possess a haploid chromosome number of about 30. Thus, the experimental species have relatively small chromosome numbers. This study showed that metaphase I bivalents in both Lepidoptera species are polykinetic; attachment of kinetochore microtubules is found scattered throughout the entire poleward chromosomal surface. The microtubules were inserted in material of medium electron density. A pair of distinct kinetochore plates, consisting of material of about the same electron density as the chromatin, was detected at each poleward chromosomal surface in metaphase I bivalents of the caddis-fly, L. decipiens. The observations suggest that DNA elements responsible for the organization of the kinetochores are dispersed throughout the chromosomes in the two Lepidoptera species, whereas they are narrowly clustered in the Trichoptera. Thus, karyotype evolution in the closely related Lepidoptera and the Trichoptera involved widely differing mechanisms.

Centromeric dots in crane-fly spermatocytes: meiotic maturation and malorientation.

During the first meiotic division in crane-fly spermatocytes, the two homologs of a metaphase bivalent each bear two sister kinetochores oriented toward the same pole. We have previously reported treatments that increase the percentage of metaphase bivalents in which one or both homologs have bipolar malorientations: kinetochore microtubules extending from a homolog toward both poles. The maloriented homologs lag at anaphase. Treatments that induce this behavior include: (a) recoverey from exposure to low temperatures or Colcemid or Nocodazole concentrations that prevent spindle formation but allow nuclear membrane breakdown, and (b) exposure to 6 degrees C, a temperature that permits spindle assembly but slows progression through meiosis. Giemsa staining methods reveal two 0.5 micron diameter dots at the centromeric region of each metaphase homolog; these often are more separated in maloriented homologs. This investigation was undertaken to assess whether this separation precedes the establishment of bipolar malorientation, and hence may be a cause of it, or is only a consequence of forces resulting from bipolar malorientation. Analysis showed that, in untreated cells, the average center-to-center distance between sister centromeric dots increases during the course of meiosis I. After the above-mentioned treatments, center-to-center distances similar to those normally seen in untreated half-bivalents at anaphase I were seen in bivalents, both after and before nuclear membrane breakdown. Longer exposure to temperatures that arrested meiosis increased the degree of dot separation. Based on our data, we conclude that normal orientation during the first meiotic division is aided by the close apposition of centromeric dots, and that a time-dependent maturation occurs causing centromeric dots to separate for the second meiotic division and facilitating orientation of sister kinetochores to opposite poles. If centromeric maturation occurs either prior to or during early stages of the first meiotic division, then it may contribute to persisting bipolar malorientation.

Meiosis, SC-formation, and karyotype structure in diploidPaeonia tenuifolia and tetraploidP. officinalis

The meiosis of the diploidPaeonia tenuifola and the allotetraploidP. officinalis was studied after conventional methanol/acetic acid-fixation and synaptonemal complex (SC) spreading. Meiosis inP. tenuifolia (2n = 10) is normal with five bivalents in metaphase I, and the SCs in pachytene show regular features. InP. officinalis (2n = 4x = 20) univalents, bivalents and multivalents are found in metaphase I. The SCs reveal several abnormalities: a high number of unpaired lateral elements, partner exchanges between three and four lateral elements, loops and lateral element thickenings. These characteristics are compared with the situations found in other polyploid and hybrid species. It is noteworthy that the abnormalities in meiosis ofP. officinalis are not reflected in its somatic karyotype. Its features were analysed after silver staining and fluorescent staining with chromomycin and compared with those ofP. tenuifolia.

Bivalent orientation and behavior in crane-fly spermatocytes recovering from cold exposure.

At metaphase in crane-fly primary spermatocytes, the two sister kinetochores at the centromere of each homologue in a bivalent normally are adjacent and face the same pole; one homologue has all its kinetochore microtubules (kMTs) extending toward one pole and its partner has all its kMTs extending toward the opposite pole. In contrast, during recovery from exposure to 2 degrees C, one or both homologues in many metaphase bivalents had bipolar malorientations: all kMTs of one kinetochore extended toward one pole and some or all those of its sister extended toward the other. Metaphase sister kinetochores that had most of their kMTs extending toward the same pole were adjacent, and those with most extending toward opposite poles were separated from each other. Distances between homologous centromeres were similar to those in properly oriented bivalents. Maloriented bivalents were tilted relative to the spindle axis, and analysis of living cells showed that tilted configurations were rare during prometaphase in untreated cells but frequently arose in cold-recovering cells as initial configurations, then persisted through metaphase. This was in contrast to unipolar configurations of bivalents (configurations suggesting orientation of both homologous centromeres toward the same pole), which always reoriented shortly after the configuration arose. We conclude that in cold-recovering cells, bipolar malorientations are more stable than unipolar malorientations, and the orientation process is affected such that bipolar malorientations arise in bivalents upon initial interaction with the spindle and persist through metaphase.

Malorientation in half-bivalents at anaphase in crane fly spermatocytes following Colcemid treatment.

Addition of Colcemid to the medium in which larvae of the crane fly Nephrotoma suturalis are cultivated induces a number of anomalous patterns of chromosome segregation. One of these is the anaphase lagging of autosomal half-bivalents. To investigate the cause of anaphase lagging, the orientation of sister kinetochores in Colcemid-treated spermatocytes having lagging half-bivalents was analyzed in serial sections. In contrast to nonlaggard half-bivalents that had pure syntelic orientation (sister kinetochores having all of their kinetochores microtubules (KMTs) extending to the same pole), six of the seven autosomal laggards that were selected for analysis had kinetochores with either amphitelic orientation (sister kinetochores each with a bundle of KMTs extending to opposite poles) or merotelic orientation (a single kinetochore having KMTs extending toward both poles). An additional laggard had syntelic orientation but two of the microtubules that were in its kinetochore fiber passed through the kinetochore and extended beyond it toward the equator. The bipolar malorientations observed in anaphase half-bivalents are interpreted to be a cause of the anaphase lagging induced by Colcemid treatment. Furthermore, it is hypothesized that such bipolar malorientations also may be stabilized at metaphase and thus explain the unusual tilting of metaphase bivalents commonly observed in Colcemid-treated cells.

Absence of chiasmata from the heteromorphic region of chromosome I during spermatogenesis in Triturus cristatus carnifex

Analysis of squash preparations of spermatocytes from crested newts, Triturus cristatus carnifex, has shown that in most cells at least one large bivalent regularly fails to form chiasmata in one arm-pair. Feulgen microphotometry of diplotene and metaphase bivalents has shown that it is the largest bivalent in each cell which shows chiasma failure in one arm-pair. A C-banding technique which identifies chromosome I by virtue of a long, darkly stained region in its long arm, was used to confirm the absence of chiasmata from one arm-pair of the longest bivalent, and specifically from the darkly stained region. The achiasmate region which chromosome I exhibits during spermatogenesis, corresponds to the “heteromorphic region” of oocyte lampbrush bivalent I in which chiasmata never form. A possible correlation between the complete absence of crossing-over from the heteromorphic region and unusual cytological and molecular features which it exhibits, are discussed.

Cytogenetics of oysters.

The paper reports a comparative chromosomes study of six species of Crasso-strea and three of Ostrea. Of these, six species occur in Karachi, West Pakistan and three on the Pacific coast of the U.S.A. Chromosomes of 18 males and 92 females were examined from germ-line cells and early embryonic mitoses.Meiosis was found to be chiasmate and photographs of first metaphase biva-lents of spermatocytes are being published for the first time. A 2n=20 (n=10) is common to all oysters. Karyotypes contain only metacentric (M) and sub-metacentric (S) chromosomes and are symmetrical and outwardly identical. Fluctuations were observed, however, in the frequencies of M and S elements in different species and have been attributed to pericentric inversions or centric shifts.

The Male Chromosomes ofCiona Intestinalis

The haploid number, n = 14 was determined in the male cells of Ciona intestinalis from the Lagoon of Venice. The pachitene and metaphase bivalents are described with regard to their length, total a...

CHIASMATIC AND ACHIASMATIC MEIOSIS IN AFRICAN EUMASTACID GRASSHOPPERS.

1. Male meiosis follows an entirely normal course in six species of the grasshopper genus Amatonga (Eumastacidae, Euschmidtiinae). 2. In twenty-four species of the Eumastacid subfamily Thericleinae the usual diplotene and diakinesis stages are omitted completely in the male sex, the transition from pachytene to prermetaphase being direct and apparently very rapid. 3. In some of these species chiasmata become visible at the beginning of first metaphase, when the spindle is established. In others the early metaphase bivalents are worm-like structures in which no chiasmata can be seen until mid-metaphase, when the chiasmata are suddenly revealed as loops open out between them. We call the latter type of meiosis cryptochiasmate. 4. In three species of the genus Thericles chiasmata are never seen in the male, even in late metaphase, and observations on first anaphase make it quite improbable that crossing-over has occurred. However, only observation of structurally heterozygous bivalents (which do not occur naturally in these species) will decide this question for certain. 5. In the species which most clearly lacks chiasmata in the male the chromosomes in the oocyte show clear chiasmata (oogenesis has not been studied in the other species).

Evolution and Variation in <i>Trillium</i>

The mechanisms of sterility were investigated with three interspecific hybrid species of Trillium found in Japan.There were three possible mechanisms concerned in sterility operative during microsporogenesis of these plants: 1) univalent formation, 2) non-dis-junction of dicentric and acentric chromatids produced in bivalents formed by a pair of corresponding chromosomes belonging to a pair of different genomes included in the hybrids, and 3) random assortment of chromosomes in dyads due to random disjunction of the bivalents formed by heterogenetic chromosome pair.The first mechanism is effective in hybrids with an odd number of different gametic sets. The latter are operative irrespective of polyploid of hybrids.It was assumed from the above that all possible interspecific hybrids of Japanese Trillium, both living and extinct, are sterile due to the above mentioned mechanisms.The origin of the dicentric chromatids, which are the cause of the second sterile mechanism, was discussed on the basis of comparative examinations of the types and frequencies of the dicentrics in all the fertile and sterile species of Japanese Trillium. The conclusion was reached that a majority of the dicentrics originate from inversion crossing-over at prophase. The simultaneous chromatid breakages at chiasmata in metaphase bivalents and the subsequent illegitimate reunion of the broken ends sometimes deform the configuration of chromatids at chiasmata in such a way as that described by Matsuura (1950). But the deformation seems to be facilitated only when the dicentrics produced by inversion crossing-over pre-exist.

The Occurrence of Unpaired Chromosomes in Hybrids Between Varieties of <i>Triticum vulgare</i>

The frequency of pollen mother cells with univalent chromosomes at first metaphase was determined in five varieties and ten varietal hybrids of vulgare wheats. The proportion of cells with univalents in the varieties varied from 2.9 per cent to 9.7 per cent and in the hybrids from 5.2 to 39.1 per cent. Hybrids between related varieties on the whole gave lower univalent frequencies than those between unrelated varieties, but exceptions occurred.In any cell with univalents two was the most common number, and as high as eight were observed. Trivalents and tetravalents were seen only rarely.Wide variation in percentage of cells with univalents was observed in some instances. Higher univalent frequency occurred in first metaphase cells from anthers in which most of the cells were well past metaphase.No significant difference in univalent frequency was found in two groups of Marquis plants kept under fairly constant temperatures the respective means of which were 60° and 77°F.The univalents in different cells were of different sizes and shapes. In certain hybrids with high univalent frequency, the univalents seemed to be longer than in certain varieties. Attenuated bivalents and bivalents with fewer chiasmata were more frequent in hybrids with frequent univalents.Typical metaphase bivalents are drawn and the number of chiasmata estimated for each. Terminal or terminal and closely sub-ter-minal chiasmata are the rule but exceptions occur. Configurations resembling some of those interpreted by HUSKINS and by POWERS as trivalents are here interpreted as bivalents.It is to be expected that the occurrence of univalents will give rise in the next generation to plants with abnormal chromosome numbers and to disturbed genetic ratios.The relationship of these observations to the chiasma theory is discussed and it is concluded that they support DARLINGTON's theory which ascribes the occurrence of univalents to a reduction in frequency of chiasmata.