Frances E. Arrighi

Localization of repetitive DNA in the chromosomes of Microtus agrestis by means of in situ hybridization

Heterochromatin in the European field vole, Microtus agrestis, was studied using a special staining technique and DNA/RNA in situ hybridization. The heterochromatin composed the proximal 1/4 of the short arm and the entire long arm of the X chromosome, practically the entire Y chromosome and the centromeric areas of the autosomes. By using the DNA/RNA in situ hybridization technique, repeated nucleotide sequences are shown to be in the heterochromatin of the sex chromosomes.

The structure and behavior of the nucleolus organizers in mammalian cells

The regularly occurring secondary constrictions on metaphase chromosomes of mammalian cells prove to be nucleolus organizers as expected. The expression of nucleolus organizers as secondary constrictions, however, varies from cell to cell and from tissue to tissue, including cultivation in vitro. Electron micrographs of the organizer region show that the nucleolus organizer at metaphase is not a constriction. The width of the organizer area is the same as the condensed chromosomal arms; but the filaments, which are the major components of this region, show a diameter of 50–70 Å. The condensed chromosome arms consist of filaments 150–200 Å in diameter. In some mammalian species, structures similar to the nucleolus organizer are located at the end of chromosomes. These may be terminal nucleolus organizers.

The sex chromosomes of the Chinese hamster; constitutive heterochromatin deficient in repetitive DNA sequences

Portions of constitutive heterochromatin of the Chinese hamster Cricetulus griseus, do not appear to contain a disproportionately high amount of repeated DNA sequences. These specific regions are the long arm of the X chromosome, the entire Y chromosome, and the centromeric region of chromosome 10. Other heterochromatic areas of the Chinese hamster chromosomes showed localization of repetitious DNA.

Buoyant densities of DNA of mammals

One characteristic of DNA, CsCl buoyant density peak values, was determined for DNA samples isolated from 93 species belonging to 11 orders of mammals. The CsCl buoyant density values varied over a very narrow range, 1.696–1.701 g/cm3. Satellite DNAs were found in a number of species. The function and origin of these satellite DNAs are not known.

Chromosomal Evolution in the Genus Peromyscus (Cricetidae, Rodentia)

The diploid number of species and subspecies in genus Peromyscus is 48. The number of total chromosome arms (fundamental number), however, varies from 56 to 96. Apparently the changes were accomplished by reciprocal translocations and pericentric inversions, but not by the Robertsonian process.

Repetitive DNA of Gallus domesticus and its cytological locations

Abstract DNA of the domestic chicken, Gallus domesticus , was fractionated by sonication, denaturation and reassociation on hydroxyapatite column. The reassociated repetitious DNA fraction comprises 17% of the genome and showed 2 distinct peaks in neutral CsCl density gradients. In situ hybridization using 3 H-RNA complementary to the various repetitive DNA fractions showed that the microchromosomes and the W chromosome had a disproportionately high content of repetitive DNA and that the two types of chromosomes contained different fractions of repetitive DNA.

Isolation and characterization of DNA from fixed cells and tissues

Abstract DNA was isolated from cultured mammalian cells, liver tissue and Escherichia coli after treatment with the common laboratory fixatives for various periods of time. The cultured cells included the mouse cell strain LM and the Chinese hamster cell strain Don C. Liver tissue was obtained from young adult Chinese hamsters. Ultraviolet spectral absorbance ratios, CsCl buoyant density determinations, melting curves and hyperchromicity were used to characterize the DNA samples. Recovery of “normal” DNA was excellent with most fixatives, but not when formalin was used. Formalin fixation interfered with the isolation procedure, and when DNA was extracted the buoyant densities in CsCl were significantly different from the DNA extracted from unfixed materials, but the Tm values were not different.

Automated homologue matching of human G-banded chromosomes

Two sets of human G-banded chromosomes were employed to test a computer algorithm for homologue matching. One set was produced at the Rigshospitalet, Copenhagen, and the other at the University of Texas M. D. Anderson Hospital. Employing a cross-correlation measure to select candidate homologue mates for each chromosome resulted in correct matches in 91.1% of the cases in the Anderson set and 93.1% in the Denmark set. To identify each chromosome and to give a measure of classification accuracy when performed by humans, five cytogeneticists were asked to independently karyotype the 49 cells in the Anderson set. Agreement between two cytogeneticists was measured by the kappa statistic. If all chromosomes that could not be identified by any given cytogeneticist were removed from the comparison, kappa values were found to be in the vicinity of 0.95. With such unidentifiable chromosomes included as a separate class, the kappa values were closer to 0.89.

Distribution of repetitious DNA in human chromosomes

Studien von in situ DNS/RNS-Hybriden (oder Mischflüssigkeiten) zwischen RNS und verschiedenen Fraktionen von DNS und Metaphase-Chromosomen des Menschen ergaben, dass hauptsächlich die wiederholt vorkommende DNS-Fraktion C o t = 0 → 0.005 sich in der centromeren und telomeren Region befindet.

Chromosomes of the tree shrews (Tupaiidae)

Chromosomes from seven species of Tupaiidae, including Tupaia glis , T. chinensis , T. longipes , T. montana , T. minor