Chromomere Pattern Research Articles

Karyotyping of Amoeba proteus

In this paper, the protocol which we have developed to get satisfactory spreads of Amoeba proteus mitotic chromosomes is presented, and the process of karyotyping this amoeba species is described. This protocol allows obtaining of extended chromosomic with repeatable chromomeres pattern in individual chromosomes. We have shown that metaphase in «B»-strain amoebae (one of the type strains of A. proteus in the Amoebae Strains Collection at the Institute of Cytology) contains 27 chromosome pairs with homologous chromomeric pattern. It is ascertained that chromomeric pattern is chromosome-specific feature. The bank of images of DAPI- and YoYo1-banded individual metaphase chromosomes of «B»-strain of A. proteus is presented.

Mapping of pachytene bivalents of female codling moth Cydia pomonella (Linnaeus) (Lep., Tortricidae)

AbstractSpread pachytene nuclei of codling moth Cydia pomonella (Linnaeus) (Lep., Tortricidae) females of a Syrian strain (SY) were used to investigate chromomere patterns of chromosome bivalents and determine their length. The karyotype of female codling moths consists of 28 chromosome bivalents, of which seven are clearly distinguishable using chromosome length and the number and size of the chromomeres in the pachytene stage. One autosome bivalent has two nucleolar organizing regions (NORs) that are located at the opposite ends of the chromosome and appear as distinct structural landmarks. In female codling moths, the WZ sex chromosome bivalent was easily identified in pachytene oocytes according to the heterochromatic thread of the W chromosome. This study contributed to the knowledge and identification of pachytene chromosomes of female codling moths.

Amplification of ribosomal DNA in Acheta

Photometric measurements of DNA in Acheta domesticus were made on single nuclei and on each pachytene chromosome, chromomere by chromomere. The extinction values were processed by a computer. The background is negligible and there is good agreement between the chromomere pattern and the amount of DNA found. The 2C value of Acheta brain nuclei is 4.0 pg. The following DNA values were obtained for oocyte nuclei at early pachytene. (1) All DNA bodies or major chromomeres 4.18 pg. (2) The chromosomes only, 9.11 pg. (3) The amplified major chromomere of chromosome 6, 2.00 pg. (4) The major chromomere of chromosome 11, 1.48 pg. The 11 pachytene chromosomes of the oocytes contain 0.4, 0.3, 0.3, 0.2, 0.2, 0.2, 0.1, 0.1, 0.1, 0.1 and 0.1 X 109 nucleotide pairs respectively (haploid value). The amplicon (the site of amplification) of chromosome 6 contains 0.02 pg whereas that of chromosome 11 has 0.01 pg (haploid value); this corresponds to 0.02 X 108 and 0.01X 109 nucleotide pairs respectively. In the case of chromosome 6, the amplified major chromomere contains 1.9-2.5 X 109 nucleotide pairs, which is circa 100 times the DNA of its amplicon (haploid). An average pachytene chromomere (haploid) in Acheta has 0.01 X 109 nucleotide pairs. The location in specific chromomeres of well-defined genes such as the cistrons for 28S and 18S ribosomal RNA, coupled with knowledge of the number of nucleotide pairs in these chromomeres helps to elucidate the organization and function of the genetic units in eukaryotes.

Action of restriction endonucleases on the DNA and chromosomes of Muntiacus muntjak.

The restriction enzymes EcoR1, Hpa II and Hae III have been used to cleave nuclear DNA of Muntiacus muntjak. Each enzyme gives rise to a different pattern. Each pattern is characterized by the presence or absence of bands and by the type of distribution of most of the sequences cleaved. Hpa II and Hae III cleave DNA segments which are CCGG and GGCC respectively but they produce quite different patterns with the same DNA. Hpa II builds a gradient of large molecules concentrated mainly between 11.0times103 and 600 base pairs whereas Hae III forms a smear of small molecules concentrated mainly between 3.4times103 and 200 base pairs. This difference in pattern is characteristic of the DNA of over 30 eukaryotic species so far investigated. The action of Hae III on fixed metaphase chromosomes of M. muntjak leads to the appearance of a “hairy” structure and a chromomere pattern which is not present in the controls and which does not show up after EcoR1 treatment. The effect of the enzyme on the chromosomes is not understood at present.

Karyotype Evolution by Chromosome Fusion in the Moth Genus Orgyia

Chromosome numbers vary greatly in Orgyiu, from low numbers, like n = 11 in O.thyellina and n = 14 in O.antiqua, to a high number, n = 30, as in O.recens and O. ericue. Meiotic synapsis was regular in O. thyellina and O.antiqua; 11 and 14 normal bivalents, respectively, were found in meiosis. The paired homologues displayed homologous chromomere patterns. In the species hybrid between antiqua and thyellina, many synapsed chromosome segments were found in meiosis. This indicates sufficient segmental homology between chromosomes of the two species although the paired pachytene chromosome segments rarely displayed similar chromomere patterns. Chromosomes switched pairing partners, thus forming multivalents, linked by chiasmata in males, and long synaptic chains in the achiasmatic females. Multivalent formation is understood as the consequence of a separate evolution of the two species from a species with a high chromosome number. Multiple chromosome fusions resulted in similarly low chromosome numbers but different segmental compositions of the chromosomes in the two species.

Cytogenetics of a Moth Species with a Low Chromosome Number, Orgyia Thyellina

While most Lepidoptera have numerous small chromosomes, Orgyia thyellina has few (n = 11) and relatively big chromosomes. We exploited this situation in a light microscopic study of chromosome morphology in mitosis and in various stages of male and female meiosis.—There is no indication of a primary constriction in mitotic chromosomes. Meiosis is chiasmatic in males and achiasmatic in females. Bivalents in the late female pachytene stage have a chromomere pattern of an unusually high degree of resolution. It is especially suited to test structural homology of synapsed chromosomes in bivalents. The chromomere pattern is homologous in the synapsed autosomes but partly differential in the equally synapsed sex chromosomes. The female pachytene affords a good basis for cytogenetic investigations in Lepidoptera.

Chromomeric pattern of maize pachytene chromosomes after trypsin treatment.

The bivalent chromomeres of maize were analyzed by means of enzymatic treatment with trypsin. The aim was to verify if the effect of swelling observed in human meiotic chromosomes also occurs in these bivalents, and if this morphological change allows a greater visual resolution of the chromomeric pattern. Bivalents treated with trypsin showed a structure with sequential and linear distribution of small rings. Comparisons between bivalent morphology, treated and non-treated, indicated a collinearity among the sequences of rings and the chromomeres. The results obtained were considered useful to analyze and to make a chromomere map. This treatment can also provide cytological evidence that may help to understand the pairing process. It was concluded that the ring-shape was caused by trypsin-induced "disjoining" just in the chromomeric but not in the interchromomeric regions.

Sex chromosome differentiation in some species of Lepidoptera (Insecta).

Sex chromosome morphology of eight Lepidoptera species was studied, exploiting predominantly the pachytene stage when chromosomes display a remarkable chromomere pattern. Six species had a WZ/ ZZ sex chromosome system, one species a W1W2Z/ ZZ system and one species was of the Z/ZZ type. Much like XY chromosomes in groups with male heterogamety, the lepidopteran sex chromosomes showed various degrees of structural differentiation. Differences between Z and W chromomere patterns ranged from undetectable to obviously non-homologous. A common property of the W chromosomes (the W1 in the W1W2Z/ZZ system) was the possession of a block of heterochromatin. The heterochromatin block comprised a small or a large segment of the W or even the entire W, depending on the species. Segments with apparent structural homology are evolutionarily young parts of the sex chromosomes-recently fused autosomes that have not had sufficient time for differentiation. The 'primitive' lepidopteran species Micropterix calthella had a Z/ZZ sex chromosome system. This supports the hypothesis that the lepidopteran W chromosome came into being at the base of the 'advanced' Lepidoptera; it was presumably an autosome whose homologue fused to the original Z chromosome.

Preparation of tomato meiotic pachytene and mitotic metaphase chromosomes suitable for fluorescencein situ hybridization (FISH)

Fluorescence in situ hybridization (FISH) is an increasingly powerful tool with a variety of applications in both basic and applied research. With excellent genetic, cytogenetic and molecular maps available, the tomato genome provides a good model to benefit from the full potential of FISH. Tomato chromosomes at mitotic metaphase are small and not particularly suitable for high-resolution FISH. In contrast, chromosomes at meiotic pachytene are about 15 times longer, and easier to identify by their differences in chromosome arm lengths and chromomere pattern. We have developed a technique for preparing chromosomal spreads of young pollen mother cells at mid-prophase I which is suitable for FISH. In a first series of experiments, the hybridization patterns of three classes of repetitive DNA sequences were studied in single and multicolour FISH.

5-Azadeoxycytidine induced undercondensation in the giant X chromosomes of Microtus agrestis

Fibroblasts of female Microtus agrestis were treated with 5-azadeoxycytidine (5-aza-dCyd) at a final concentration of 10(-5) M during the last 2 h of culture. This cytidine analogue induces distinct undercondensation of the constitutive heterochromatin in the giant X chromosomes. The undercondensed heterochromatic thread exhibits longitudinal segmentation reminiscent of a chromomere pattern. In the late-replicating X chromosome, 5-aza-dCyd also inhibits condensation of the genetically inactivated euchromatin (facultative heterochromatin). The described effects of 5-aza-dCyd on the X chromosome structure appear to be incorporation independent.

The Use of Tangled Pachytene Chromosomes for Karyotype Analysis in Atylosia

Species of plants in which pachytene chromosomes are not readily Identifiable because of chromosome tangling present difficulties for karyotype studies. A method of analysis that overcomes this problem was used to prepare karyotypes of two Australian relatives of the pigeon pea (Cajanus cajan): Atylosia acutifolia and A. pluriflora. Quantitative description of the major chromomeres of the chromosomes, together with keys and idiograms, has made it possible to characterize and identify chromosomes with the microscope. The major chromomeres of Atylosia were larger than those of pigeon pea, the largest being a 12-part cluster for A. acutifolia, whereas the largest for A. pluriflora was a 6-part cluster. The chromomere patterns of the two accessions of A. acutifolia showed large differences, suggesting that these two accessions may be representative of subspecies. It is anticipated that our data on chromomere patterns of Atylosia will find application in the identification of chromosomes in interspecific hybrids between pigeon pea and Atylosia. The method also should be applicable to other species in which chromosome tangling makes karyotype analysis difficult.

Pachytene Chromosome Morphology inCoffeaL. I. Nucleolar Chromosomes

SUMMARYA morphological analysis of the nucleolar chromosomes in pachytene was carried out in ten species of the genus Coffea L. introduced in Brazil. This analysis showed that the nucleolar chromosomes of these species differs particularly in total length, arm ratio and chromomere pattern. Seven of the diploid species have one nucleolar chromosome attached to only one nucleolus, and two species have two chromosomes attached to only one nucleolus. The only polyploid species in the genus, C arabica L., also has two chromosomes attached to one nucleolus. Morphological features between these two chromosomes indicates a probable similarity between the genomes that constitute the C. arabica complement.

Karyotype, heterochromatin content and meiotic features ofPoecilocera picta (Orthoptera, Acrididae)

Cytological study of three distinctly separated populations ofPoecilocera picta revealed a chromosome number of 2N = 18 + XO/ XX. Except for the hemizygosity of a procentric heterochromatic block in the M6 pair of the Bangalore population, the basic karyotype of the three populations is markedly similar. The autosomal karyotype formula is 2Lt + 4Mt + 1 Mst + 2S st and the telocentric X chromosome is the longest of the complement. All bivalents at pachytene carried procentric heterochromatic blocks. The M4 is the nucleolus organiser with the NOR region situated interstitially but proximal to the centromere. About 11 µm (4%) of the total (290 µm) autosomal pachytene complement is heterochromatic; a major portion of it is contributed by the S9 pair which is mostly heterochromatic. Chiasmata are localized proximally and distally and in the S9 pair their formation is confined to the short procentric euchromatic segment of the long arm. Female meiosis did not reveal any chromomere pattern at pachytene and, unlike in the male, the sex bivalent in the female is indistinguishable from the autosomal bivalents. G- and C-banding patterns in males showed procentric bands in all the chromosomes. In addition there are eight telomeric and two interstitial bands which are C negative. The S9 pair showed only two bands. The G-banding pattern of the sex chromosome in meiosis showed only a centric band while the heterochromatic body of the facultatively heterochromatic X remained G negative.

Pachytene chromosome identification by a key based on chromomeres in the pigeonpea

A method for the preparation and utilization of the pachytene chromosome karyotype of the pigeonpea is presented. Major chromomeres, most of which were compound structures, were used to characterize individual chromosomes. The karyotype was prepared from a large number of cells showing only one or a few analyzable chromosomes, rather than scarce cells showing the entire chromosome complement. As all 11 chromomere patterns were identified in each of two cells showing all 11 chromosomes clearly, this indicated that the entire genome had been described. A key, based on distribution and structure of major chromomeres, provides a rapid means of identification and comparison.

Transplantation of insect giant chromosome nuclei into amphibian oocytes.

Polytene salivary gland nuclei of Chironomus pallidivittatus were transplanted into oocytes of Xenopus laevis which were then cultured in vitro for 18 h. The giant chromosomes and nucleoli as well as the entire nuclei enlarged considerably in volume during this time. The polyteny and specific chromomere pattern of the chromosomes were maintained, and the puffing of the salivary gland-specific Balbiani rings was not noticeably changed. - Polytene nuclei from differentiated insect cells transplanted into Xenopus oocytes thus appear suited for exposing giant chromosomes in vivo to purified factors such as regulatory molecules.

Studies on centromere, chromomere and nucleolus in pachytene nuclei of rice, oryza sativa, microsporocytes.

Pachytene nuclei of rice microsporocytes were examined about centromere constitution, chromomere pattern and nucleolar situation by flame drying method and Giemsa stain. Uridine treatment of intact microsporocytes before preparation distinctly revealed the centromere on late pachytene chromosomes, that is, four equal entities were detected in a centromeric region.Chromosomes treated in KCl solusion were stained clear enough to be analysed their chromomere patterns on 12 bivalents. Mid-pachytene chromosomes were suitable for chromomere analysis and capable of discriminating 12 bivalents with their chromomere patterns, centromere position and length.Supernumerary micronucleoli were frequently observed in a pachytene nucleus besides a macronucleolus. They were situated in three conditions; free from chromosomes, adhered to the surface of various intervening sites of chromosomes and adhered to the ends of chromosomes. In some nuclei micronucleoli appeared to be excised out from macronucleoli were noticed. These observation indicated the origin of micronucleoli.

Pachytene analyses in Atylosia sericea and Cajanus cajan*A. sericea hybrid.

On the basis of relative length, arm ratio, chromomere pattern and nucleolar association all the eleven pachytene chromosomes of A. sericea were identified. The pachytene complement consists of 2 median, 8 submedian and 1 subterminal chromosomes. On the basis of comparison of parental pachytene chromosomes, 7 are common to A. sericea and Cajanus. Complete synapsis in majority of the microsporocytes of Cajanus×A. sericea hybrid indicates a high degree of homology. In the hybrid, out of eleven bivalents, eight bivalents, including two exhibiting heteromorphism were identified. Occasionally two translocations and a duplication loop were observed in a few cells. On the basis of various evidences, it is concluded that A. sericea has a lesser degree of affinity to Cajanus than A. lineata.

Pachytene analyses in Atylosia scarabaeoides and Cajanus cajan*A. scarabaeoides hybrid.

All the eleven pachytene chromosomes of A. scarabaeoides were identified on the basis of their relative length, arm ratio, chromomere pattern and nucleolar association. The pachytene complement of A. scarabaeoides consists of one median, 9 submedian and one subterminal chromosomes. On the basis of direct comparison of parental pachytene chromosomes, 7 chromosomes are common to A. scarabaeoides and C. cajan. In 8 bivalents of the hybrid the homoeologues participating in pairing were identified. Out of these 8, one bivalent showed non-homologous association and 4 were found to be heteromorphic. Two translocations and an interstitial duplication were noticed in a few microsporocytes. On the basis of the common chromosomes involved in translocations and those exhibiting heteromorphism in the 2 hybrids, C. cajan×A. sericea and C. cajan×A. scarabaeoides but not in the C. cajan×A. lineata hybrid it is concluded that A. sericea and A. scarabaeoides are closer to each other than either of them to A. lineata.

The cytogenetics of F1 hybrids from Oryza nivara Sharma et Shastry * O. sativa L.

IRRI Accession 101508 of the wild species Oryza nivara Sharma et Shastry was crossed directly and reciprocally to six varieties of the cultivated species, O. sativa L. This accession was cross-compatible with the six O. sativa cultivars.Each of the parents and hybrids have median, submedian, and subtelocentric chromosomes. A combination of three median (chromosome number 2, 3 and 7), seven submedian (number 1, 4, 5, 8, 9, 11 and 12), and two subtelocentric chromosomes (number 6 and 10) were the most common set. The parents and hybrids differed markedly in their chromomeric pattern, chromatin length, and arm ratio.The most frequent chromosomal aberrations observed were loose pairing at pachytene, univalents, and quadrivalents at diakinesis and metaphase I, bridges and late disjunction at anaphase I, and bridges and laggards at telophase I.Based at pollen and spikelet counts, only O. nivara, O. nivara×TNl and O. nivara×Dgwg were partially sterile. The other F1 hybrids were fertile. The difference between the pollen and spikelet sterilities in most hybrids and parents may be due to environmental effects. There was no direct relationship between the meiotic aberrations observed and the sterility of the F1 plants.Chromosome pairing was essentially normal in all F1 plants and most of them are fertile, indicating that the O. nivara accession and the O. saliva cultivars have the same genome composition (AA). There is close affinity between IRRI Acc. 101508 and the O. sativa cultivars.

Chromosome structure and function in man. VI. Pachytene chromomere maps of 16, 17 and 18; pachytene as a reference standard for metaphase banding.

Pachytene maps of chromosomes 16, 17, and 18 have been constructed and are illustrated diagrammatically and in comparison with photomicrographs of representative bivalents. Their relative lengths and arm ratios are similar to the corresponding values at metaphase. Bivalent 17 is characterized by overall pale staining relative to that of the remainder of the autosomal complement; it also exhibits a region of heavily compacted chromatin situated medially in its long arm, unlike 16 and 18, each of which has a compacted region adjacent to the centromere. Structural polymorphism was not observed during this study. Comparison between these maps and the corresponding diagrams (Paris Conference, 1971, Supplement, 1975) of metaphase G-banding provides a quantitative estimate of the increment of structural detail present at pachytene. There is a general compatibility between the two types of pattern, strongly suggesting that bands represent aggregates of adjacent chromomeres. For these reasons, and because chromomere patterns are of natural occurrence, pachytene is suggested as a reference standard for chromosome structural differentiation visualized at metaphase. A number of different methods are known to effect additional metaphase banding detail. Most of these are not widely used, even though there is need for finer detail in the visual or cytophotometric analysis of increasingly more subtle rearrangements of the genome. Some examples are given.