Morphology Of Pachytene Chromosomes Research Articles

Cytological Studies in Digitaria pentzii Stent

Fourteen accessions of Digitaria pentzii have been studied cytologically: Ten of them are tetraploids, two are triploids, one is a diploid and one is a aneuploid. Observations made on chromosome configurations at diakinensis and metaphase 1 in polyploids, together with preliminary studies on gross morphology of pachytene chromosomes, indicate that the tetraploids are allopolyploids and the triploids are autopolyploids. Elimination of chromatin material through B-chromosome process following translocation is cited as one of the mechanisms for the occurrence of aneuploids.

FISH mapping and molecular organization of the major repetitive sequences of tomato

This paper presents a bird's-eye view of the major repeats and chromatin types of tomato. Using fluorescence in-situ hybridization (FISH) with Cot-1, Cot-10 and Cot-100 DNA as probes we mapped repetitive sequences of different complexity on pachytene complements. Cot-100 was found to cover all heterochromatin regions, and could be used to identify repeat-rich clones in BAC filter hybridization. Next we established the chromosomal locations of the tandem and dispersed repeats with respect to euchromatin, nucleolar organizer regions (NORs), heterochromatin, and centromeres. The tomato genomic repeats TGRII and TGRIII appeared to be major components of the pericentromeres, whereas the newly discovered TGRIV repeat was found mainly in the structural centromeres. The highly methylated NOR of chromosome 2 is rich in [GACA](4), a microsatellite that also forms part of the pericentromeres, together with [GA](8), [GATA](4) and Ty1-copia. Based on the morphology of pachytene chromosomes and the distribution of repeats studied so far, we now propose six different chromatin classes for tomato: (1) euchromatin, (2) chromomeres, (3) distal heterochromatin and interstitial heterochromatic knobs, (4) pericentromere heterochromatin, (5) functional centromere heterochromatin and (6) nucleolar organizer region.

The "A" genome of Arachis hypogaea L.

An attempt was made to find out the possible donor of the ‘A’ genome in Arachis hypogaea. For this, the chromosome morphology at pachytene was studied in Arachis correntina (Burk) Krap. et Greg. (Unpub. PI 331194) a diploid member of section Arachis. A comparison was also made of chromosome associations at meiotic metaphase I, chiasma frequencies, meiotic abnormalities, pollen fertilities and agronomical features of triploid, tetraploid and hexaploid derivatives from the two crosses A. hypogaea×A. correntina and A. hypogaea×A. chacoense. Pachytene chromosome morphology of A. correntina conformed to the ‘A’ genome of A. hypogaea. The derivatives also did not differ from each other. The tetraploid derivatives were similar to those of A. hypogaea parent for the various characters studied, except for the fact that the derivatives had leaf spot and rust resistance incorporated into them from the wild species. It was concluded that A. correntina could also be a donor of the ‘A’ genome and that genomic differences between section Arachis diploid species with the exception of A. batizocoi are not much pronounced.

A preliminary pachytene analysis of two species of Arachis L.

The morphology of pachytene chromosomes was studied in A. glabrata Benth. and A. pusilla Benth. belonging respectively to the sections Rhizomatosae and Triseminale. These two species can not be crossed with the cultivated groundnut A. hypogaea L. All 20 chromosomes of A. glabrata could be identified individually and further classified into 5 basic types. The features that enabled the identification of chromosomes were: total length, arm ratios, nucleolus attachment and position and extent of heterochromatin. A simple key has been proposed for classifying different chromosomes to facilitate their easy identification. The genomes of A. glabrata did not resemble those of A. hypogaea except for the presence of an 'A' chromosome, 2 euchromosomes and 2 nucleolus organisers. A. glabrata did not appear to be an amphidiploid but rather an allopolyploid hybrid. The genome of A. pusilla contained chromosomes unlike those of any other species of section Arachis. It was concluded that both these species are quite unrelated to other species of the section Arachis.

Chromosome morphology in species of the sections, Erectoides and Extranervosae of the genus Arachis L.

Chromosome morphology at pachytene was studied in two species; A. sp. (GKP 9990, Section. Erectoides) and A. villosulicarpa (Section. Extranervosae) and compared with the other sectional species. The genus Arachis appeared to be based on a basic karyotype of six differentiated chromosomes, three specialised chromosomes and one nucleolus organizer. The karyotypes of species belonging to sections Erectoides, Triseminale and Extranervosae appeared to be more primitive than sections Arachis and Rhizomatosae. The section Arachis appeared to be a natural group of cross-compatible species having the characteristic A chromosome with the exception of A. batizocoi. The pachytene chromosome morphology did not indicate a highly marked chromosomal differentiation between the A' and ‘B’ genomes assumed to be present in the cultivated groundnut. Specific differences have been thought to be brought about in the genus Arachis through minor structural repatterning and major genetic differentiation.

Pachytene chromosomes of Physalis lanceifolia Nees.

Pachytene chromosome morphology of the haploid complement of P. lanceifolia Nees (n=12) was studied. They are characterised by the presence of heterochromatic and euchromatic segments. An idiogram was constructed based on chro-mosome length, lengths of heterochromatic and euchromatic segments and arm ratios. Chromosome 11 has the nucleolus organiser in the totally heterochromatic short arm.

Zea diploperennis

The cytogenetic analysis of Zea diploperennis, diploid perennial teosinte (n = 10), Is presented and compared cytologically to that of the tetraploid perennial teosinte. Pachytene chromosome morphology and meiosis of the F1 hybrid of diploperennis and the WMT maize stock show a paracentric inversion in chromosome 5 and a terminal inversion in chromosome 9. Both the diploid and tetraploid perennials have the same small terminal knobs (or prominent telomeres) on otherwise knobless chromosomes and both have the chromosome 9 inversion.

Identification of the chromosomes of groundnut, Arachis hypogaea L.

Morphology of pachytene chromosomes was studied in Spanish (TMV-2) and Virginia (M-13) types of groundnut. All the 20 chromosomes could be identified individually from certain diagnostic characters in addition to their total lengths and arm ratios. A simple key has been proposed for classifying the different chromosomes to facilitate their easy identification. The ‘A’ chromosomes described earlier were found to correspond to a small chromosome that was completely heterochromatic. The ‘B’ chromosomes were traced to a bivalent with 2 large heterochromatic segments in the short arm. Chromosome morphology was more or less similar in both the varieties.

Pachytene chromosome morphology of diploid Cynodon dactylon (L.) Pers.

Diploid clones of C. dactylon were studied to determine their pachytene chromosome morphology. The chromosomes ranged in length from 20.5μm to 44.6μm. Arm ratios ranged from under 1.50 to 2.14. The chromosomes were identified by their arm length ratios, relative length and position and number of prominent chromomeres. The shortest chromosome was designated chromosome 1 and other chromosomes numbered on basis of average chromosome length. There was little variability in chromosome morphology among clones.

Pachytene chromosome morphology with reference to sex instability in Ricinus communis L.

The morphology of the pachytene chromosomes of Ricinus communis L. (2n=20), the castor plant, was examined and compared, using light microscopy, in two sex forms, one having an apical distribution of pistillate flowers (wild type), the other having a uniform distribution of pistillate flowers (mutant). Nonreverted mutants resulting from sex instability of the wild type did not display microscopically discernable alterations in chromosome morphology.

Nucleolar organizing chromosomes ofRicinus

Pachytene chromosome morphology was compared in nine races ofRicinus communis L. (2n = 20), using pollen mother cells (PMCs) and light microscopy. Of the ten bivalents, only the two possessing nucleolar organizing regions (NORs), chromosomes 2 and 7, exhibit structural variations among the races. The NORs are located in the short arms of these two chromosomes. Most of the observed structural variations affect these short arms, which are similar morphologically and consist largely of heterochromatic segments. The PMCs contain a single nucleolus and this is associated with the NOR of each of the two chromosomes at a particular frequency in each race. In eight races, a nucleolar constriction (NC) is present in either chromosome 2 or chromosome 7. In these races, the nucleolus is associated with the chromosome possessing an NC at a frequency of 100% and with the chromosome lacking an NC at a frequency ranging between 5.6 and 100%, depending upon the race. No microscopically visible NC is present in the ninth race. In this race, the nucleolus is associated with both chromosomes 2 and 7 at a frequency of 100%. The association of the nucleolus with a chromosome possessing an NC is at the NC and with a chromosome lacking an NC is at the terminal heterochromatic segment of the short arm. Several interpretations are offered to account for the variations in frequency of association between the nucleolus and each of the nucleolar organizing chromosomes. It is suggested that the two non-linked NORs have evolved through some intragenomic changes rather than polyploidy, that this species is highly intolerant to structural variations other than those occurring in or near the NORs, and that structural variations in the nucleolar organizing chromosomes are not associated with racial variations in plant phenotype.

Morphology of the pachytene chromosomes of Physalis pubescens L.

Pachytene chromosome morphology of P. pubescens L., (n=12) was studied. The twelve chromosomes were identified individually high lighting their diagnostic features and an idiogram, constructed on the basis of total chromosome length, lengths of chromatic and achromatic segments and arm ratios, was provided. Chromosome 8 has the nucleolus organiser in the totally chromatic short arm.

Trisomics from triploid-diploid crosses in self-incompatible Lycopersicum peruvianum

An attempt was carried out to produce trisomics of the wild tomato L. peruvianum, to define their essential features, and to detect relationships between trisomy and the expression of self-compatibility.Triploid-diploid crosses in L. peruvianum yielded nearly 40% aneuploids. Of these, 18% were single trisomics, and the rest had 2, 3 and 4 extra chromosomes. Almost all the trisomics occurred in crosses where the triploid was used as female parent. Vigour and fertility of trisomics were not much different from those of disomics, and morphologically they were very similar.The extra chromosome was identified in three self-compatible trisomic plants through somatic and pachytene chromosome morphology. One of these plants was trisomic for chromosome 1, while the other two were trisomic for chromosome 3. In these trisomics a positive correlation was found between chromosome length and trivalent formation, but no relationship between chromosome length and frequency of laggards was observed.A series of test-crosses revealed that the capacity of the trisomics to produce seed upon selfing always resulted from alterations of the incompatibility phenotype of the style and not from competitive interaction in the pollen. Progeny analyses showed that the self-compatibility features of the trisomics were not transmitted from one generation to the next. The implications of these findings are discussed.

Pachytene Chromosome Morphology and Its Bearing on Interspecific and Intergeneric Relationships of Coix

Pachytene Chromosome Morphology and Its Bearing on Interspecific and Intergeneric Relationships of Coix

Morphology of pachytene chromosomes and its bearing on the nature of polyploidy in the cytological races of Apluda mutica L.

Pachytene chromosomes of diploid (n=10), hexaploid (n=30) and heptaploid (n=35) races of Apluda mutica L. are similar in their diagnostic morphological features. Hexaploids and heptaploids possess the same ten basic types of chromosomes characteristic of the diploid in multiples of six and seven respectively. Quadrivalent associations involving four homologous chromosomes were observed for all ten types of chromosomes of the hexaploid and heptaploid. It is suggested that the polyploid races may be autoploids.

Pachytene chromosome morphology at different ploidy levels in Medicago

Pachytene chromosome morphology at different ploidy levels in Medicago

Morphology of the pachytene chromosomes of the Indian diploidSolanum nigrum L.

The pachytene chromosome morphology of a locally occurring diploid form ofSolanum nigrum L. (n=12) was studied. The pachytene chromosomes are charaterised by the presence of (1) chromatic and achromatic segments, (2) distinct centromeres and (3) macrochromomeres (telomeres) terminating the chromosome arms. The twelve bivalents are identified individually and described.

Morphology of Pachytene Chromosomes in Pearl Millet

Morphology of Pachytene Chromosomes in Pearl Millet

Studies on pachytene chromosomes in the genusDigitaria

Observations on gross morphology of pachytene chromosomes in nine accessions ofDigitaria comprising six species have been made. Based on the morphology of chromosomes at pachytene they have been grouped into four different types. Occurrence of 18-chromosome types inD. decumbens, D. macroglossa andD. valida has been reported for the first time. A comparative study of pachytene chromosome morphology amongst the diploids and between diploid and tetraploids in conjunction with the taxonomical studies has been suggested as a means for obtaining information towards the understanding of the origin, evolution and identification of parental species of several tetraploids. The information so obtained would ultimately benefit the forage breeding programme.