Chromosome Recognition Research Articles

Supernumerary Chromosomes in Saxifraga virginiensis (Saxifragaceae)

Acetocarmine squashes of root tips have demonstrated that 2n = 20 and 38 in Saxifraga virginiensis. These contrast with the earlier reported count of 2n = 28 for this species. In several populations supernumerary chromosomes were detected. Both intrapopulational and interpopulational variation in supernumerary chromosome number were detected, with the largest number of supernumerary chromosomes observed being six. Because these supernumerary chromosomes are equal in size to many of the smaller A chromosomes during mitotic metaphase, the presence of supernumerary chromosomes in this species could not be ascertained by analysis of mitotic metaphase preparations alone. During mitotic prophase, however, the supernumerary chromosomes of S. virginiensis are highly heterochromatic, appearing more densely coiled and darkly stained than the A chromosomes. This characteristic facilitated the recognition of supernumerary chromosomes in this species. The similarity in size of A and supernumerary chromosomes during mitotic metaphase and the observation of six supernumerary chromosomes in one population suggest that the count of 2n = 28 reported earlier for S. virginiensis may actually be a misinterpretation of 2n = 20 plus 8 supernumerary chromosomes. Furthermore, these findings and the observation of this same supernumerary chromosome phenomenon in other species of Saxifraga raise the possibility that some of the many disparate chromosome counts attributed to aneuploidy in the large genus Saxifraga may also be the result of misinterpretations of supernumerary chromosomes as A chromosomes.

SUPERNUMERARY CHROMOSOMES IN SAXIFRAGA VIRGINIENSIS (SAXIFRAGACEAE)

Acetocarmine squashes of root tips have demonstrated that 2n = 20 and 38 in Saxifraga virginiensis. These contrast with the earlier reported count of 2n = 28 for this species. In several populations supernumerary chromosomes were detected. Both intrapopulational and interpopulational variation in supernumerary chromosome number were detected, with the largest number of supernumerary chromosomes observed being six. Because these supernumerary chromosomes are equal in size to many of the smaller A chromosomes during mitotic metaphase, the presence of supernumerary chromosomes in this species could not be ascertained by analysis of mitotic metaphase preparations alone. During mitotic prophase, however, the supernumerary chromosomes of S. virginiensis are highly heterochromatic, appearing more densely coiled and darkly stained than the A chromosomes. This characteristic facilitated the recognition of supernumerary chromosomes in this species. The similarity in size of A and supernumerary chromosomes during mitotic metaphase and the observation of six supernumerary chromosomes in one population suggest that the count of 2n = 28 reported earlier for S. virginiensis may actually be a misinterpretation of 2n = 20 plus 8 supernumerary chromosomes. Furthermore, these findings and the observation of this same supernumerary chromosome phenomenon in other species of Saxifraga raise the possibility that some of the many disparate chromosome counts attributed to aneuploidy in the large genus Saxifraga may also be the result of misinterpretations of supernumerary chromosomes as A chromosomes.

Ultrastructural analysis of the X1X2X3O sex chromosome system during the spermatogenesis of Tegenaria domestica (Arachnida).

An ultrastructural study was performed on the sex chromosomes (male X1X2X3O) during the spermatogenesis of Tegenaria domestica (Arachnida, Agelenidae). This study was carried out using random and serially cut sections. During pachytene and diplotene the three X chromosomes are longitudinally paired. Each of these consists of a central core of condensed chromatin, surrounded by a field of dense chromatin projections through which the chromosomes are in contact with one another. These projections may be responsible for the recognition and pairing of the sex chromosomes and in some way participate in their non-disjunction during anaphase I. A study of the structure and behaviour of the sex chromosomes during spermatogenesis is also presented. The available information on non-synaptonemal complex-mediated chromosome pairing and a systematization of sex chromosome structure in spiders are discussed.

Chromosome Counts, Cytology, and Reproduction in the Cactaceae

Chromosome counts and observations of reproduction for 55 taxa of Cactaceae indicate that polyploidy is correlated with self-fertility, adventive embryony, profuse branching, and vegetative reproduction. Six genera (Blossfeldia. Cleistocactus, Frailea, Pelecyphora, Rebutia, and Strombocactus) and 35 species or varieties are reported here for the first time. Preliminary observations of pachytene and diplotene indicate that these stages may be more useful in chromosome recognition than mitotic stages. Secondary association at metaphase I and II is interpreted as a retention of homologue association at interphase I and II (interkinesis). During meiosis of certain species, Feulgen negative bodies are present. The production of an abnormal premeiotic division is suggested as a mechanism for polyploid origin.

CHROMOSOME COUNTS, CYTOLOGY, AND REPRODUCTION IN THE CACTACEAE

Chromosome counts and observations of reproduction for 55 taxa of Cactaceae indicate that polyploidy is correlated with self‐fertility, adventive embryony, profuse branching, and vegetative reproduction. Six genera (Blossfeldia. Cleistocactus, Frailea, Pelecyphora, Rebutia, and Strombocactus) and 35 species or varieties are reported here for the first time. Preliminary observations of pachytene and diplotene indicate that these stages may be more useful in chromosome recognition than mitotic stages. Secondary association at metaphase I and II is interpreted as a retention of homologue association at interphase I and II (interkinesis). During meiosis of certain species, Feulgen negative bodies are present. The production of an abnormal premeiotic division is suggested as a mechanism for polyploid origin.

A technique for multiple-cell chromosome karyotyping.

A new approach to a system for chromosome karyotyping is presented. The system assembles the information about chromosomes from several cells at a time, thereby filtering out noise due to variations in the slide preparations. The system makes i possible to use metaphase spreads which are incomplete due to missing chromosomes, touching and overlapping chromosomes and stain particles. The system gives a precise description of the chromosome complement in terms of distribution function parameters, with the uncertainty of the parameters specificed. The system is adaptive with respect to the initial reference parameter set so that both recognition of normal chromosomes, in spite of the variation displayed among individuals, and identification of aberrant chromosomes are possible. The precise chromosome descriptors can be used to detect differences between the tested individual and various references, in order to find chromosomal abnormalities.

A method for analysis of chromosomes in hybrid cells employing sequential G-banding and mouse specific C-banding

A sequential banding technique is described for the identification of chromosomes of interspecific hybrid cells with a mouse parent. Metaphases were first G-banded using trypsin-Giemsa to identify individual chromosomes and then the centromeres of the same cells were differentially stained by a C-banding technique specific for mouse chromosomes. This mouse specific C-banding employs treatment with hot formamide-SSC before staining, and the effect of this treatment on the staining of chromosomes from a number of species was investigated. The specific staining of mouse centromeres confirms the parental origin of chromosomes identified by G-banding and allows the rapid recognition of mouse and non-mouse chromosomes in metaphases from many different hybrid combinations.

Giemsa C-Banding and the Evolution of Wheat

The somatic chromosomes of common wheat, Triticum aestivum L. (2n = 6x = 42), and those of two of its diploid progenitors and T. speltoides, have been individually identified by a Giemsa staining technique. In wheat, telocentric chromosomes were used to aid the recognition of individual chromosomes, and an ideogram has been constructed depicting the C-band positions. There is no similarity in the C-banding of chromosomes within a homoeologous group, with the possible exception of group 5. Comparisons of the C-banding of the diploid species T. monococcum, T. speltoides, and T. tauschii with that of the A, B, and D genomes, respectively, in hexaploid wheat corroborate that T. speltoides could not be the donor of the B genome to wheat and that T. monococcum and T. tauschii are the probable donors of the A and D genomes, respectively.

TELOMERIC ASSOCIATIONS OF GAMETIC AND SOMATIC CHROMOSOMES IN DIPLOID AND AUTOTETRAPLOIDORNITHOGALUM VIRENS

In acetocarmine root-tip squashes, diploid cells of Ornithogalum virens in prophase exhibit configurations resulting from end-to-end associations of the six chromosomes. Homologues lie opposite one another in a ring. Prophase chromosomes of the autotretraploid cells likewise associate end-to-end; however, four homogues instead of two generally lie adjacent to one another and four (or eight) ends are often connected instead of the two (or four) found in diploid cells. Prophase chromosomes in a haploid pollen grain of a diploid form an open chain of three chromosomes, whereas in pollen from the autotetraploid balanced gametes form a configuration in which homologous pairs lie adjacent to one another and are attached end-to-end to other homologous pairs of nonhomologous chromosomes to form a chain. These observations are discussed in terms of the role telomeric associations may play in recognition and pairing of homologous chromosomes during meiotic prophase. This recognition of homologues may occur as early as syngamy.

Identification of mammalian chromosomes.

ABSTRACT Quantitative cytochemistry in the form of microspectrophotometry can be of help in chromosome recognition. In most mammals, among them man, the sensitivity of these methods is, however, not sufficiently high. Fluorometric techniques permit the application of twice as high microscope resolution and many times higher sensitivity in quantitative work, when dealing with substances with suitable fluorescence. A technique, working with fluorescence microscopy and fluorometry has been developed for the identification of mammalian chromosomes. For instance, in man all 22 autosome pairs and the X- and Y-chromosomes can be recognized. The technique also considerably improves the possibilities of observing and identifying chromosome aberrations of different kinds. The fluorescence of the Y-chromosome can be observed also in interphase nuclei and can thus be of use in the determination of genetic sex. A considerable number of DNA-reacting fluorescent agents have been tested. The best results have been obtained with quinacrine and quinacrine mustard. Sorting of chromosomes can in most cases be done visually after photography. More detailed information can be obtained by microfluorometry. Computerized analysis of the fluorescence patterns of the human chromosomes has shown a great statistical significance of the shape of these patterns. This has also led to efforts towards automated sorting of chromosomes. Several other techniques have recently been developed for chromosome banding, some giving patterns closely resembling the quinacrine patterns. The methods have been applied to many problems of medical genetical interest. They have also been used for analysis of the karyotypes of several other mammals and of somatic cell hybrids. Work on some plant material indicates that some types of heterochromatic regions have characteristic fluorescence properties.

Factors affecting recognition and disjunction of chromosomes at distributive pairing in female Drosophila melanogaster. I. Total length vs. arm length.

The behavior of a compound metacentric fourth chromosome (see PDF) has been examined to determine whether arm length or total length is the basis for recognition in distributive pairing. Recognition was judged by the frequency with which the (see PDF) nondisjoined from a series of X duplications (Dp), ranging in size from </= 0.3 to > 4 times the size of a single fourth chromosome. Dp, (see PDF) nondisjunction was measured in the absence and in the presence of a competitor, a compound metacentric X. In both situations, total length and not arm length, was found to confer the characteristic recognition property to the (see PDF). A comparison of Dp, (see PDF) nondisjunction curves for both the noncompetitive and competitive situations with analogous Dp, 4 curves previously obtained, show the Dp, (see PDF) curves to be similar in shape to those obtained earlier but displaced one unit to the right, corresponding precisely to the difference in size between the (see PDF) and the 4. Rules governing chromosome recognition for acrocentrics were found completely applicable to metacentrics; disjunctive behavior of metacentrics differed from that of acrocentrics in that two arms conferred on a chromosome the capacity to act as the intermediate of a trivalent when size no longer warranted this attribute. This capacity, itself, is size-dependent.

Centromere localization at meiosis and the position of chiasmata in the male and female mouse

Techniques for obtaining differential Giemsa staining of the paracentromeric (p.c.) regions of male and female mouse meiotic chromosomes (centromeric heterochromatin) were explored and standard procedures developed for the different meiotic cells in the two sexes. The best result followed the use of heat at controlled pH in Sorensen's phosphate buffer or in Standard Saline Citrate (SSC) solutions. With these techniques, morphological features of the p.c. regions and their variation were studied in normal animals (CFLP strain) and in a strain (AKR) homozygous for a centric fusion [T(11; ?)-1 Ald] between chromosomes No. 6 and No. 15 (Miller et al., 1971). The Y chromosome was often found to show distinct p. c. staining at first and apparently at second meiotic metaphase, and the X and Y chromosomes were found to associate as bivalents by their long arms. Autosomal p.c. regions showed variation in size which might indicate differences between non-homologous chromosomes but a tendency to similarity between homologues. Differences were found between males and females in respect to proportions and variation of bivalents with single and double chiasmata. The relative positions of chiasmata were different in the two sexes. The presence of the centric fusion in the males did not seem to affect the pairing behaviour of the remaining autosomes or of those taking part in the centric fusion. The possibility is discussed that the p.c. regions, to which also other functions would seem to appertain, may be important for chromosome recognition and pairing, possibly on a quantitative basis.

END-TO-END, CHAIN-LIKE ASSOCIATIONS OF PAIRED PACHYTENE CHROMOSOMES OF CREPIS CAPILLARIS

Studies on the pachytene stage of meiosis of Crepis capillaris showed that the paired chromosomes are attached end-to-end forming chain-like configurations. The arrangements of the chromosomes in these tandem associations are according to the expectations based on the somatogram of this species. These observations make it very likely that the end-to-end chromosome associations present in all somatic interphase cells (Wagenaar, 1969) have their primary significance in the recognition and pairing of homologous chromosomes during early meiotic prophase.

Lampbrush chromosomes of crested newtsTriturus cristatus(Laurenti)

Lampbrush chromosomes of crested newts<i>Triturus cristatus</i>(Laurenti)