Small Submetacentric Chromosomes Research Articles

Intra-individual variations of chromosomes and DNA content in meristems of adventitious roots ofOrnithogalum umbellatumL.

SUMMARYThe 92 bulbs from a population of Ornithogalum umbellatum which is stable at 2n = 2x = 18, are characterized by a karyotype containing one pair of large metacentric chromosomes, five pairs of large telocentric chromosomes and three pairs of small submetacentric chromosomes; only, two meristematic root cells of one bulb show aneuploidy (2n = 19 and 2n = 25). Although the mean DNA content measured in metaphase plates of meristematic cells of adventitious roots from a single bulb is highly variable (up to 50% difference); in the two cases where aneuploidy was encountered very little or no increase in DNA content was observed.

Karyotype analyses reveal inter-individual polymorphism and association of nucleolus-organizer-carrying chromosomes in Capros aper (Pisces: Zeiformes)

Three different karyomorphs with 2n=46, 2n=44 and 2n=42 for Capros aper (L., 1758) (Zeiformes) collected from the Gulf of Lion, near Banyuls-sur-Mer, France, in July 1990 were determined. Karyomorphs were characterized by the same arm number [Fundamental number (FN)=50], suggesting that chromosome variations are due to Robertsonian fusions. In somatic metaphase spreads stained with silver nitrate, nucleolus organizer regions (NORs) consistently occupied a terminal position on the short arms of two small submetacentric chromosomes. Ca. 30% of silver-stained metaphases in each specimen showed NOR chromosomes associated in pairs by their nucleolus organizer regions.

Fluorescent chromosome banding inLarix leptolepis (Pinaceae)

The somatic karyotype ofLarix leptolepis (2n=24) is composed of 12 large metacentric chromosomes and 12 small submetacentric chromosomes. Each CMA-band appeared at the interstitial region of four metacentric chromosomes. Each bright DAPI-band appeared at the proximal region of one side of the arms of nearly all chromosomes. However, two submetacentric chromosomes had no discriminable DAPI-bands. The CMA-bands coincided in position with the secondary constriction and the negative DAPI-bands.

Chromosomes of gaur cross domestic cattle hybrids

The chromosomes of five gaur (Bos gaurus hubbacki) domestic cattle (B indicus cross B taurus) hybrids (three females, two males) were studied using the leucocyte culture method and centromeric (C) banding technique. All the hybrids had a diploid chromosome number of 2n = 58, made up of two submetacentric autosomes (different in size) and 54 acrocentric autosomes, most of which could be arranged in pairs in descending order of size. The sex (X) chromosomes in females were a pair of submetacentric chromosomes smaller than the submetacentric autosomes. The Y chromosome in males was a small submetacentric chromosome. The C banding patterns were useful in identifying the X and Y chromosomes and the inherited submetacentric autosomes from the gaur sire. Phenotypically, the hybrids resembled normal B indicus cross B taurus calves except for the presence of a distinct hump-like dorsal ridge containing the spinous processes of the third to 11th thoracic vertebrae, upright 'deer-like' ears and long lean legs. The potential of these hybrids as important genetic resources for meat production is stressed.

High frequency of translocation heterozygotes in odd year populations of pink salmon (<i>Oncorhynchus gorbusch</i><i>a</i>)

The pink salmon (<i>Oncorhynchus gorbuscha</i>) has a rigid two year life cycle so that populations spawning on the even years do not hybridize with populations spawning on the odd years. Examination of the chromosomes of two populations from an even year (1986) and four populations from an odd year (1987) showed that all individuals from the even year populations had a diploid number’of 52, considered the normal number for the species, while a high frequency of individuals in each of the odd year populations sampled from Washington State to Alaska were translocation heterozygotes with a diploid chromosome number of 53. The chromosome involved in the translocation was the seventh metacentric pair containing the NOR (nucleolus organizer region) adjacent to the centromere. In two populations a simple fission of this chromosome has produced individuals with chromosomes with two acrocentrics replacing the metacentric chromosome, with the larger acrocentric having the NOR adjacent to the centromere on the long arm. In the other two populations individuals with 53 and 54 chromosomes were found in which the acrocentric with the NOR has undergone an inversion so that the NOR is now on the short arm of a small submetacentric chromosome. In one population all of the individuals with 53 and chromosomes were of this type, while in the other case both forms were found. Because these two populations are adjacent to each other in the middle of the range sampled, the rearranged chromosome probably had a single origin.

The organisation and expression of histone genes from Xenopus borealis.

We have isolated genomic clones from Xenopus borealis representing 3 different types of histone gene cluster. We show that the major type (H1, H2B, H2A, H4, H3), present at about 60-70 copies per haploid genome (1), is tandemly reiterated with a repeat length of 15 kb. In situ hybridization to mitotic chromosomes shows that the majority of histone genes in Xenopus borealis are at one locus. This locus is on the long arm of one of the small sub-metacentric chromosomes. A minor cluster type with the gene order H1, H3, H4, H2A is present at about 10-15 copies. The genome also contains rare or unique cluster types present at less than 5 copies having other types of organisation. An isolate of this type had the gene order H1, H4, H2B, H2A, H1 (no H3 cloned). Microinjection of all of the clones into Xenopus laevis oocyte nuclei shows that most of the genes present are functional or potentially functional and a number of variant histone proteins have been observed. S1 mapping experiments confirm that the genes of the major cluster are expressed in all tissues and at all developmental stages examined.

Characterisation of a very complex constitutive heterochromatin in two Gerbillus species (Rodentia).

A large amount of heterochromatin is observed in two species of the genus Gerbillus, G. nigeriae and G. hesperinus. The C-band material represents about one-half of the total karyotype length in the former species, and about one-third in the latter. Several banding techniques and various 5-bromodeoxyuridine (BrdU) treatments were used to characterise these heterochromatic segments. After applying the R-banding technique, three different staining responses of the heterochromatin can be distinguished. In G. nigeriae, strongly stained segments (R-band positive) appear in most chromosomes and, in particular, constitute the short arms of all the larger chromosomes. Palely staining heterochromatic segments (R-band negative) are less abundant in G. nigeriae but predominate in G. hesperinus. In addition, in both species an intermediate staining of heterochromatin is observed near the centromere or in the heterochromatic short arms of some acrocentric and small submetacentric chromosomes. Very short BrdU treatment during the end of the last cell cycle results in asymmetrical staining of chromatids in heterochromatic segments after applying the acridine orange or FPG (fluorescence plus Giemsa) technique. The alternating location of strongly staining segments in one or the other chromatid simulates sister chromatid exchanges ("pseudo-SCE"). This pattern persists after longer BrdU treatment during different stages of the last cell cycle and is independent of the R-staining properties of the heterochromatin. The lateral asymmetric appearance of the large heterochromatic segments in Gerbillus is interpreted as reflecting an uneven distribution of adenine and thymidine between the two strands of DNA.

Chromosomal composition of four permanent cultured cell lines derived from human gliomas

Four permanent cell lines derived from malignant human gliomas were karyotyped using Giemsa-trypsin banding. D-65 MG had a stemline with 44 chromosomes, including 11 markers: 1p+, 2q−, 3p−, 3q+, 4p−, 9q−, 11q+, 15q−, 17p+, 21p+, 22q−. The net effect after accounting for fragments in markers was: +8, −10, −16 −X. D-32 MG had chromosome counts 90–91 without a distinct stem karyotype. Modal cells contained from 3 to 5 copies of the normal autosomes and 5 markers: 1q−, 3q−, 7q−, 13q−, 18q−. D-32 MGCl 2 had a complex karyotype containing 78–82 chromosomes. There was no stemline, and modal cells varied from one another primarily in their set of marker chromosomes. A total of 23 markers were seen in this line, 17 of which were present in most modal cells. They were partially characterized as: 1q+, 1q+, 2q−, 5q+, 7p−, 7q−, 8p+, 8p+, 9p+, 12p+, 14q−, 16q+, 19q+, 19p+, a small submetacentric chromosome of undetermined origin and two small isochromosomes, i(Dp or Gp) and i(17p or 18p). A-172 MG had a modal peak of 77 chromosomes within which no two cells were exactly alike. Ten markers seen in modal cells were: 1p−, 4p+, 6p+, 6p+, 6q−, 7p−, 9p−q+, 13q+ 14p+, 22q+. There were no normal copies of chromosomes #1, #6, #9, #14. These four glioma-derived cell lines possess unique karyotypes, but each displays some combination of the numerical and structural deviations generally associated with established glioma lines.

Chromosome polymorphism in Japanese sika, Cervus (Sika) nippon.

Chromosome examination by blood culture was conducted on 35 Japanese sika, Cervus (Sika) nippon, revealing that the number of chromosomes varied according to individuals, such as 65, 66, 67 and 68. This numerical variation depended on the presence or absence of large metacentric chromosomes and submetacentric chromosomes in the autosomes. It was possible to observe six karyotypes according to the presence or absence of these two kinds of chromosomes. Polymorphism of these chromosomes is presumed to be formed when either large metacentric chromosomes or submetacentric chromosomes are formed following fusion of four acrocentric chromosomes in the autosomes at the centromere. The fundamental number was constant, 70 in all cases. This is considered to be due to the so-called Robertsonian translocation. The common phenomenon observed in all the individuals examined was the presence of one pair of middle-sized metacentric chromosomes in the autosomes. The X-chromosome was the largest among the acrocentric chromosomes and the Y-chromosome could be easily identified as a small submetacentric chromosome.

Intraspecific chromosomal variation within Galago crassicaudatus (Galaginae)

Differences in the karyotype of Galago crassicaudatus crassicaudatus and Galago crassicaudatus argentatus are presented. Both subspecies have the same diploid number (2n = 62), including 3 pairs of small submetacentric chromosomes and 1 pair of medium-sized acrocentric chromosomes with small satellites, a submetacentric X and an acrocentric Y chromosome. The karyotype of G. c. crassicaudatus contains 10 medium-sized subacrocentric and 16 acrocentric chromosome pairs; G. c. argentatus only 3 medium-sized subacrocentric and 23 acrocentric chromosome pairs. Our observations are compared with and discussed in relation to previously reported karyotypes of G. crassicaudatus subspecies.

The nucleolar chromosome in embryos of Rana pipiens

Karyotype analyses of prometaphases from medullary plate cells derived from mid-neurulae of Rana pipiens have led to the identification of the nucleolar chromosome and nucleolar organizing region, which is located on the longer arm of a small sub-metacentric chromosome (No. 10).

Chromosomal banding patterns in Akodon arviculoides (2n=14),Akodon sp.(2n=24 and 25), and two male hybrids with 19 chromosomes.

Chromosomal polymorphism resulting from two pericentric inversions in Akodon arviculoides (2n=14) has been described (YONENAGA, 1972a). In this paper the banding patterns are presented and identification of the inverted segments of the autosomal pairs 2 and 3 is made. The karyotype of Akodon sp., which varies in diploid number (2n-24 and 25), is described and shown to be due to the presence of a small submetacentric chromosome in the 2n=25 individuals. The karyotypes of two 2n=19 males studied show that they are hybrids between Akodon arviculoides (2n=14) and Akodon sp. (2n=24).

Chromosomal banding pattern and idiogram of the cotton rat, Sigmodon arizonae (Rodentia, Muridae).

A procedure for obtaining G-bands on chromosomes of mammals is outlined. The procedure was utilized in an investigation of the idiogram and banding pattern of the mitotic chromosomes of the cotton rat, Sigmodon arizonae. The diploid number of this species is 22, and each pair of homologues is easily separated on the basis of size, centromeric position, and banding pattern. The autosomes are represented by four pairs of large submetacentric chromosomes, three pairs of medium to small submetacentric chromosomes, two pairs of large subtelocentric chromosomes and one pair of small acrocentric chromosomes. The X chromosome is acrocentric and averages from 5.42% to 5.46% of the haploid female complement. The Y chromosome is a minute acrocentric and easily separated from the smallest acrocentric autosome. The usefulnes of Sigmodon arizonae as a laboratory animal for cytogenetic studies is substantiated.

Cat-eye syndrome, a partial trisomy 22.

A family is presented in which a phenotypically normal mother and her healthy daughter both had abnormal children with a small supernumerary chromosome. Both had clinical symptoms suggestive of cat-eye syndrome. In both women 1 G-chromosome was found to be replaced by a small submetacentric satellited chromosome. Its fluorescence pattern was compatible with that of a chromosome 22, and so was the fluorescence pattern of the supernumerary chromosome in one of the phenotypically abnormal children. Since complete monosomy G in addition to partial autosomal trisomy would not be compatible with clinical “normality” the respective karyotypes must be interpreted as a small deletion of a chromosome 22 in the healthy mother and daughter and a partial trisomy 22 in their abnormal children. Therefore it can be concluded that a deletion of a chromosome 22 is compatible with a normal phenotype and that the cat-eye syndrome results, at least in this family, from a partial trisomy 22.