Banding pattern of human chromosomes

Mitotic chromosomes

Our understanding of the structure and function of mitotic chromosomes has come a long way since these iconic objects were first recognized more than 140 years ago, though many details remain to be elucidated. In this chapter, we start with the early history of chromosome studies and then describe the path that led to our current understanding of the formation and structure of mitotic chromosomes. We also discuss some of the remaining questions. It is now well established that each mitotic chromatid consists of a central organizing region containing a so-called "chromosome scaffold" from which loops of DNA project radially. Only a few key non-histone proteins and protein complexes are required to form the chromosome: topoisomerase IIα, cohesin, condensin I and condensin II, and the chromokinesin KIF4A. These proteins are concentrated along the axis of the chromatid. Condensins I and II are primarily responsible for shaping the chromosome and the scaffold, and they produce the loops of DNA by an ATP-dependent process known as loop extrusion. Modelling of Hi-C data suggests that condensin II adopts a spiral staircase arrangement with an extruded loop extending out from each step in a roughly helical pattern. Condensin I then forms loops nested within these larger condensin II loops, thereby giving rise to the final compaction of the mitotic chromosome in a process that requires Topo IIα.

Cellular and genomic approaches for exploring structural chromosomal rearrangements

Human chromosomes are arranged in a linear and conserved sequence order that undergoes further spatial folding within the three-dimensional space of the nucleus. Although structural variations in this organization are an important source of natural genetic diversity, cytogenetic aberrations can also underlie a number of human diseases and disorders. Approaches for studying chromosome structure began half a century ago with karyotyping of Giemsa-banded chromosomes and has now evolved to encompass high-resolution fluorescence microscopy, reporter-based assays, and next-generation DNA sequencing technologies. Here, we provide a general overview of experimental methods at different resolution and sensitivity scales and discuss how they can be complemented to provide synergistic insight into the study of human chromosome structural rearrangements. These approaches range from kilobase-level resolution DNA fluorescence in situ hybridization (FISH)-based imaging approaches of individual cells to genome-wide sequencing strategies that can capture nucleotide-level information from diverse sample types. Technological advances coupled to the combinatorial use of multiple methods have resulted in the discovery of new rearrangement classes along with mechanistic insights into the processes that drive structural alterations in the human genome.

Chromosomal homology in southern Akodon

Differential staining (G and C) of southern South American Akodon are presented. A. olivaceus, A. longipilis and A. sanborni all have the same karyotype (2n = 52, NF = 58). A virtually identical band sequence is observed. This situation is interpreted using the canalization model of chromosomal evolution which stresses an optimum karyotype for each adaptive zone. Despite the high degree of conservation of the chromosome structures, the specific status of these species is supported by maintenance of distinctness when they occur in areas of sympatry.

Chromosomes and the gynecologist

Recent advances in cytogenetic techniques made a valuable contribution toward the modern practice of obstetrics and gynecology. The state of the art regarding the application of these techniques is reviewed in the following areas: the clinical features related to the various sex and autosomal chromosomal anomalies, the cytogenetics of gynecologic malignancies, the chromosomal analysis of spontaneous abortion and of parents with habitual abortions. Chromosome studies in male infertility revealed abnormalities in 11.5 per cent of 69 patients with azoospermia and 9.1 per cent of 165 patients with oligospermia. Among 77 patients with primary amenorrhea, 27.3 per cent revealed chromosomal abnormalities compared to 3.8 per cent in 103 patients with secondary amenorrhea. The term "ovotesticular dysgenesis" is used for the first time in the literature to describe a specific histologic type of streak gonad which contains ovarian stroma and dysgenetic testicular tubules.

Familial translocation t(lp--;21q+) associated with Down's syndrome

Familial occurrence of 1/21 translocation in connection with trisomy 21 was described. The possibilities of inheritance of further chromosome rearrangements arising during the gametogenesis of persons with this translocation were considered.

Dermatoglyphic patterns in trisomy 8 syndrome

Up to the present, 38 cases of trisomy 8 have been found. As most of the patients showed mosaicism, the clinical picture is variable and it seems possible that some mosaics will not be detected by the usual cytogenetic examination of blood cultures. We therefore examined the dermatoglyphics of our own case and compared the results with the findings in the other cases reported in the literature, in order to establish a typical dermatoglyphic pattern in trisomy 8 which might be useful in diagnosis. All patients exhibited several unusual dermatoglyphics, including: a low TFRC (x=96.06), high palmar (92.9%) and plantar (100%) pattern intensity, a distally placed axial triradius (62.5%), loop with accessory triradius in an interdigital area (91.7%), thenar (68.2%) and hypothenar (50.0%) patterns, simian crease (47.1%), bilateral arches on the great toes (88.9%) and hallucal-whorl (72.2%). A distinctive feature was the presence of zygodactylous triradii z, z' and z'' (100%) on the soles of the feet, and deep skin furrows on the palms and soles (68.2%). This combination of dermatoglyphic features appears to be characteristic for the trisomy 8 syndrome.

Familial occurrence of chromosome variant 17ph+

A structural chromosome variant 17ph+ was found in a high genetic risk family. The authors consider the possibility of a causal connection between minor structural changes in the karyotype and congenital defects appearing in one member of the family.

C- and G-bands of the opossum chromosomes: terminal sequences of DNA replication

The sex chromosomes of the opossum, Didelphys virginiana, are the only elements that exhibit C-banding. In contrast, the sex chromosomes as well as the autosomes bear specific G-Bands. However, unlike other mammalian species different types of G-banding are observed if the chromosomes are pretreated with trypsin and SSC solution The SSC-pretreated chromosomes show discrete bands only when stained with Giemsa at certain pH values. An asynchronous pattern of terminal DNA replication is observed among the three C-banding regions of the X-chromosome. The inter- and intrapositive G-banding areas of the chromosomes are not always late in DNA replication in comparison to those negatively stained G-banding areas.

A case of acute lymphoblastic leukemia and thorotrast-accumulation

A case of acute lymphoblastic leukemia (ALL), in a 50 years old patient, 26 years after thorotrast injection, is reported. In spite of intensive therapy, he died 2 years after diagnosis of disease. The cytogenetic showed the usual thorotrast radiation-induced abnormalities, although to a greater extent than reported in leterature. Furthermore a hypodiploidy was present, which was connected with ALL. In addition the patient exhibited the interesting phenomenon of giant satellites on one of his D14-chromosomes. This abnormally was found also in his mother and son. The question arises, how far the inherited cytogenetic pattern and the thorotrast radiation each contributed to the development of ALL.

Staining banded human chromosomes with Romanovsky dyes: some practical consequences of the nature of the stain

Chromatographic analyses of commercial samples of Romanovsky stains were followed by various chemical and staining studies. Strong banding of chromosomes was found to be favoured by the presence in the stain of high concentrations of methylene violet Bernthsen and its immediate homologues. Chromatographic analysis showed that these dyes are present in dry Leishman and Giemsa powders only in small proportion. However, additional active dye may be generated during the process of making up staining solutions from the dry powders, if the methanol used is not contaminated with formic acid and if the period of heating is not too brief.

PERICENTROMERIC CHROMOSOME BANDING IN HIGHER PLANTS

By using a modified Giemsa staining technique, which is thought to indicate the presence of repetitive DNA, pericentric heterochromatin was stained in the chromosomes of two plant species, Plantago ovata and Allium cepa. Apparently in plants, just as in animals, there is a tendency for constitutive heterochromatin and repetitive DNA to associate with chromosome centromeres.