Chromosome banding in Amphibia

High-resolution replication banding patterns were induced in prometaphase and prophase chromosomes of Xenopus laevis by treating kidney cell lines with 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT) in succession. Up to 650 early and late replicating bands per haploid karyotype were demonstrated in the very long prophase chromosomes. This permits an exact identification of all chromosome pairs of X. laevis. Late replicating heterochromatin was located by analysing the time sequence of replication throughout the second half of S-phase. Neither heteromorphic sex chromosomes nor sex chromosome-specific replication bands were demonstrated in the heterogametic ZW females of X. laevis. A detailed examination of the BrdU/dT-labelled prometaphases and prophases revealed that the X. laevis chromosomes can be arranged in groups of four (quartets), most of which show conspicuous similarities in length, centromere position, and replication pattern. This is interpreted as further evidence for an ancient allotetraploid origin of X. laevis.by H.C. MacgregorThis paper is dedicated to Prof. Wolfgang Engel on the occasion of his 50th birthday     

Chromosome banding in amphibia

A modified BrdU-Hoechst-Giemsa technique permitted the demonstration of easily reproducible replication patterns in the somatic chromosomes of Amphibia. These banding patterns allow for the first time a precise identification of all chromosomes and the analysis of the patterns of replication in the various stages of S-phase in Amphibia. Several possibilities for the use of this technique were demonstrated on three frog species of the family Ranidae, all differing greatly in their DNA-content. With this method, the homomorphic chromosome pair No. 4 in Rana esculenta could be identified as sex-specific chromosomes of the XX/XY-type. All male animals exhibit an extremely late replicating region in the Y-chromosome, which is lacking in the X-chromosome; in the female animals, both X-chromosomes replicate synchronously. These sex-specific chromosomes cannot be distinguished by other banding techniques. In the highly heteromorphic ZZ/ZW-sex chromosome system of Pyxicephalus adspersus a synchronous replication of the two Z-chromosomes of male animals and a very late replication of the short arm of the W-chromosome of female animals was demonstrated. These results support the assumption that there is no dosage compensation for Z-linked or X-linked genes by the sex chromosome inactivation mechanism in the sex chromosomes of Amphibia.     

Chromosome synapsis in hexaploids

Theoretical relationships between pachytene multivalent and bivalent frequencies in hexaploids are deduced from a model, based on chromosomes showing sequential association at equidistant pairing sites and uniform propensities for partner exchange throughout their lengths. These relationships approach a limit as the number of pairing sites tends to infinity and the intervals between them tend to zero; at the limit pairing is continuous and the quadrivalent/sexivalent ratio is at a minimum. A maximum of 34·3% of the complement is expected to form quadrivalents when there are two pairing sites per chromosome but this peak is reduced by increasing numbers of pairing sites to a limit of 29·6% when pairing is continuous. Where chromosome length is proportional to the number of pairing sites there will be a log/linear relationship between bivalent frequency and chromosome length otherwise a log/log relationship is expected. In the light of these conclusions, observations on experimental hexaploids could be used to provide estimates of the number of pairing sites on each chromosome.     

Chromosome banding in Amphibia

The somatic and meiotic chromosomes of the South American leptodactylid toads Odontophrynus americanus, Ceratophrys ornata, and C. cranwelli were analysed both with conventional staining and differential banding techniques. The karyotypes of O. americanus were tetraploid; those of C. ornata octaploid. Ceratophrys cranwelli is a diploid species whose karyotype displays great similarities with that of C. ornata. The high frequency of multivalent pairing configurations in the meioses of O. americanus and C. ornata indicate that these animals were of autopolyploid origin. The conventionally stained somatic chromosomes of O. americanus can be arranged into sets of four similar chromosomes (quartets); those of C. ornata, into sets of eight similar chromosomes (octets). The banding patterns revealed heterogeneity within some quartets of O. americanus, dividing each of them into two pairs of homologous chromosomes. In analogy, some octets of C. ornata can be subdivided into two quartets of chromosomes with homologous bands. These structural heterogeneities within the quartets and octets are interpreted as a diploidization of the polyploid karyotypes. Diploidization leads to genomes that are polyploid with respect to the amount of genetic material and diploid with respect to chromosomal characteristics and the level of gene expression. In tetraploid O. americanus, the number of nucleolus organizer regions (NORs) and their DNA content is proportional to the degree of ploidy. In contrast, up to eight NORs have been deleted in the octoploid C. ornata. These NOR losses are discussed as a possible reason for the reduction of genetic activity in polyploid genomes.This paper is dedicated to Prof. Dr. Hans Bauer on the occasion of his 80th birthday     

Chromosome Studies in Leukemia

This review discusses the significance of chromosomal abnormalities found in leukemia with the bias of belief that these have a primary role or are the mechanism of action of leukemogenic agents. The Philadelphia chromosome (Ph¹) is present in marrow cells examined without culture at any stage of most patients with chronic granulocytic leukemia (CGL). the presence of this chromosome is of diagnostic and prognostic value.Varied chromosomal abnormalities have been found in acute leukemia. Each abnormality, which may be unique, is absent in remission, found again at relapse and is seldom changed by therapy. Abnormalities may be of number of chromosomes (aneuploid) or structural rearrangements resulting in “marker” chromosomes, Ranges of abnormal numbers of chromosomes, when present, usually have related patterns which suggest origin of several cell types from one initial cell. Cells from patients with increased risk of leukemia owing to genetic factors have a high incidence of chromosome breakage and structural rearrangements suggesting a mechanism for production of clones of abnormal, possibly leukemic, cells.     

Chromosome markers in cattle

Summary Giemsa banding in cattle chromosomes enables the demarcation of both centromeric areas as pale regions and banding patterns along the chromosome arms. These are valuable in identifying all the chromosomes of a given karyotype. A high degree of intra- and inter-individual variation in the size of the centromeres was observed. This variation is useful for the identification of each individual and provides a broad base of chromosome markers for cattle breeding.     

Chromosome banding in sturgeons

The article reviews the present knowledge of chromosome banding in sturgeons and summarizes recent findings obtained by both classical banding techniques (C-banding, fluorescent and silver staining) and molecular methods, such as fluorescent in situ hybridization (FISH). The results are discussed in relation to karyotype organization and chromosome evolution in sturgeons.     

Coumarin in Chromosome Analysis

Root tips of monocotyledons were soaked 2.5-3.0 hours at 25-27° C. in saturated aqueous coumarin solution and stained in a mixture of N HC 1 and 2% aceto-orcein (1:9 by volume) 3-4 seconds over a flame. They were then squashed in 1% orcein under a cover glass, the excess stain blotted and the cover sealed. Preparations could be kept about one week. Good chromosome morphology was secured.     

Chromosome evolution in perissodactyla

Comparative painting has provided a wealth of useful information and helped to reconstruct the pathways of karyotype evolution within major eutherian phylogenetic clades. New data have come from gene localizations, BAC mapping and high throughout sequencing projects that enrich and provide new details of genome evolution. Extensive research on perissodactyl genomes has revealed not only increased rates of chromosomal rearrangements, but also an exceptionally high number of centromere repositioning events in equids. Here were combined new physical mapping, comparative painting and genome sequencing data to refine the putative ancestral karyotype maps and to revise the previously proposed scenario of perissodactyl karyotype evolution.     

Chromosome banding in Amphibia

The chromosomes of the South American marsupial frogs Gastrotheca fissipes, G. ovifera, G. walkeri and Flectonotus pygmaeus were analyzed by means of conventional and various banding techniques. The karyotypes of G. ovifera and G. walkeri are characterized by highly differentiated XY/XX sex chromosomes. Whereas the X chromosomes and autosomes contain large amounts of constitutive heterochromatin, extremely little heterochromatin is located in the Y chromosomes. This is in contrast to all previously known amphibian Y chromosomes and the Y chromosomes of most other vertebrates. In the male meiosis of G. walkeri, the euchromatic segments of the heteromorphic XY chromosomes show the same pairing configuration as the autosomal bivalents. The karyotype of F. pygmaeus is remarkable for the unique presence of telocentric chromosomes and the high frequency of interstitially located chiasmata in the meiotic bivalents. The evolution of the karyotypes and sex chromosomes, the structure of the various classes of heterochromatin and the data obtained from meiotic analyses of the marsupial hylids are discussed.     

Chromosome banding in Amphibia

The karyotype of the marsupial frog Gastrotheca riobambae is characterized by exceptionally highly differentiated XY/XX sex chromosomes. The 18S and 28S ribosomal RNA genes were found only in the nucleolus organizer region (NOR) of the X chromosome by in situ hybridization, silver staining and mithramycin banding. This amphibian species therefore exhibits a sex-specific difference in the number of ribosomal RNA genes of about 2()1(). This constitutes an extremely rare situation in the karyotype of vertebrates. Examination of various somatic tissues from female animals showed that the NORs on both X chromosomes are always active. The results are discussed in relation to the apparent absence of dosage compensation for sexlinked genes in the Amphibia.     

Chromosome pairing in maize

This report summarizes our observations at pachytene on opposite-arms intercrosses between stocks of interchanges that involve chromosomes 1 and 5 in maize.—Pairing does not begin at the centromeres in these intercrosses.—We propose a model which assumes different probability values along each chromosome arm for the initial or primary site of pairing. Observations on the frequencies of the different types of configurations at pachytene were used to estimate probability values which satisfactorily fit the data.—There is a relatively low probability (of the order of.1 to.3) for the initial pairing to be in a short terminal segment (about.1 of the arm length). Initial pairing in the one or two short segments adjacent to the tip segment is much higher. Initial pairing is much lower in segments successively closer to the middles of the chromosome arms, and then zero or nearly zero in the proximal half of the arm. This means that the initial pairing may fail occasionally even in a relatively long interchanged segment and produce a T-shaped (3-armed) configuration.—After the initial pairing has occurred, the average probability that a secondary site of pairing is adjacent to the centromere in a segment.3 to.4 the length of an arm is low (.13, ranging from.02 to.29).—We can predict that in an intercross in which both breakpoints in both parental interchanges are far out on the chromosomes, "pairs" will be formed with nonhomologous ends (homologous differential segments paired). In these pairing could have begun at any point in the interstitial segments, but not likely in segments close to the centromeres.—Multiple secondary sites which vary in time or in order of pairing will explain the variation in position of the cross-shaped pachytene configuration in interchange heterozygotes.—The observed configuration in any one cell is the result of a particular combination of pairing events at the various sites. This is a very different concept of pairing from previous interpretations which described it as a result of zipper-like action, and the variation in position of the pachytene cross-configuration as the result of "shifts" in position.—Our cytogenetic results and their interpretation are in close agreement with reports on chromosome ultrastructure and molecular events in the early stages of meiosis, i.e. the attachment of chromosome ends to the nuclear membrane, the manner in which synaptonemal complexes develop, and the regions of DNA whose replication is delayed until zygonema.     

Chromosome banding in amphibia

The chromosomes of 26 species of Anura from variously highly evolved groups were analysed with the fluorescent GC-specific antibiotics mithramycin and chromomycin A₃ as well as with the AT-specific quinacrine. The mithramycin- and chromomycin A₃-stainings generally resulted in a pattern of the constitutive heterochromatin opposite to the one obtained with quinacrine stain. The weaker a heterochromatic region fluoresces with quinacrine, the stronger is the intensity of the fluorescence achieved with mithramycin and chromomycin A₃. Some of the telomeric and interstitial heterochromatic regions, however, exhibit no enhanced fluorescence with any of the fluorochromes. The nucleolar constrictions of the nucleolus organizer regions (NORs) displayed the brightest mithramycin- and chromomycin A₃-fluorescence in the karyotypes and interphase nuclei of all species examined. The contrast of the brightly fluorescing GC-rich heterochromatin and of the NORs is considerably enhanced, when the non-fluorescent AT-specific oligopeptide distamycin A is employed as a counterstain. No banding patterns were observed with the fluorochromes in the euchromatic regions of the metaphase chromosomes; this is attributed to the strong spiralization of the anuran chromosomes. A cytochemical classification of the various chromatin types in the anuran chromosomes is discussed on the basis of the differential labelings found on the constitutive heterochromatin by means of the fluorochromes.This paper is dedicated to Professor Dr. Hans Bauer on the occasion of his 75th birthday     

Chromosome assortment in Saccharum

Recent work has revealed random chromosome pairing and assortment in Saccharum spontaneum L., the most widely distributed, and morphologically and cytologically variable of the species of Saccharum. This conclusion was based on the analysis of a segregating population from across between S. spontaneum SES 208 and a spontaneously-doubled haploid of itself, derived from anther culture. To determine whether polysomic inheritance is common in Saccharum and whether it is observed in a typical biparental cross, we studied chromosome pairing and assortment in 44 progeny of a cross between euploid, meiotically regular, 2n=80 forms of Saccharum officinarum LA Purple and Saccharum robustum Mol 5829. Papuan 2n=80 forms of S. robustum have been suggested as the immediate progenitor species for cultivated sugarcane (S. officinarum). A total of 738 loci in LA Purple and 720 loci in Mol 5829 were amplified and typed in the progeny by arbitrarily primed PCR using 45 primers. Fifty and 33 single-dose polymorphisms were identified in the S. officinarum and S. robustum genomes, respectively ( ₂ at 98%). Linkage analysis of single-dose polymorphisms in both genomes revealed linkages in repulsion and coupling phases. In the S. officinarum genome, a map hypothesis gave 7 linkage groups with 17 linked and 33 unlinked markers. Four of 13 pairwise linkages were in repulsion phase and 9 were in coupling phase. In the S. robustum genome, a map hypothesis gave 5 linkage groups, defined by 12 markers, with 21 markers unlinked, and 2 of 9 pairwise linkages were in repulsion phase. Therefore, complete polysomic inheritance was not observed in either species, suggesting that chromosomal behavior is different from that observed by linkage analysis of over 500 markers in the S. spontaneum map. Implications of this finding for evolution and breeding are discussed.     

Chromosome banding in Amphibia

The mitotic and meiotic chromosomes and interphase nuclei of the South American tree-frog Centrolenella antisthenesi were studied with various banding techniques. The karyotype is distinguished by a new category of heteromorphic XY/XX sex chromosomes in an initial stage of differentiation. In diakinesis of male meiosis the XY chromosomes exhibit the same pairing configuration as the autosomal bivalents. Analysis of the chromosomes with DNA base pair-specific fluorochromes revealed that unusual large amounts of brightly labeled AT-rich constitutive heterochromatin are located in the centromeric and pericentromeric regions of all autosomes and in the X chromosome. In most types of interphase cell nuclei the brightly fluorescent heterochromatic regions fuse to very large chromocenters.     

Chromosome banding in Amphibia

The mitotic and meiotic chromosomes of the marsupial frog Gastrotheca riobambae were analysed with various banding techniques. The karyotype of this species is distinguished by considerable amounts of constitutive heterochromatin and unusual, heteromorphic XY sex chromosomes. The Y chromosome is considerably larger than the X chromosome and almost completely heterochromatic. The analysis of the banding patterns obtained with GC- and AT-base-pair-specific fluorochromes shows that the constitutive heterochromatin in the Y chromosome consists of at least three different structural categories. The only nucleolus organizer region (NOR) of the karyotype is localized in the short arm of the X chromosome. This causes a sex-specific difference in the number of NOR: female animals have two NORs in diploid cells, male animals one. No cytological indications were found for the inactivation of one of the two X chromosomes in the female cells. In male meiosis, the heteromorphic sex chromosomes form a characteristic sex-bivalent by pairing their telomeres in an end-to-end arrangement. The significance of the XY/XX sex chromosomes of G. riobambae for the study of X-linked genes in Amphibia, the evolution of sex chromosomes and their specific DNA sequences, and the significance of the meiotic process of sex chromosomes are discussed.     

Chromosome banding in amphibia

A cytogenetic study performed on a population of the South American leptodactylid frog Eleutherodactylus maussi revealed multiple sex chromosomes of the X₁X₁X₂X₂/X₁X₂Y (=XXAA/XXA^Y) type. The diploid chromosome number is 2n=36 in all females and 2n=35 in most males. The multiple sex chromosomes originated by a centric fusion between the original Y chromosome and a large autosome. In male meiosis the X₁X₂Y (=XXA^Y) multiple sex chromosomes form a classical trivalent configuration. E. maussi is the first species discovered in the class Amphibia that is distinguished by a system of multiple sex chromosomes. Only one single male was found in the population with 2n=36 chromosomes and lacking the Y-autosomal fusion. This karyotype (XYAA) is interpreted as the ancestral condition, preceding the occurrence of the Y-autosome fusion.by H.C. Macgregor