Karyotypie diversity and taxonomic problems in the genus Arvicanthis (Rodentia,Muridae)

The analyses of R- and C-banding patterns of chromosomes of Arvicanthis niloticus originating from two different localities (Egypt and Central African Republic) revealed karyotypic differences caused by one pericentric inversion and three translocations, one being reciprocal and the others Robertsonian. There were also some differences in centromeric heterochromatin patterns.The data indicate that these two forms are distinct species, cytogenetically isolated, and that a revision of the taxonomic status of the genus Arvicanthis is needed.     

How are sticky chromosomes formed?

Blood lymphocytes in culture were irradiated by gamma-rays 3 h to 30 mn before harvesting. The various induced lesions were analysed, with a particular attention on sticky chromosomes, i.e. radial figures in which chromosomes are not obviously broken, but are linked by a tiny filament. Such anomalies are preferentially induced in mid to late G2-phase. They result from recombinations occurring at nonrandom chromosome regions: junction between hetero- and euchromatin, and telomeric regions. It is proposed that they are formed when double strand breaks are induced while intrachromatidic links have started to be formed in the course of chromosome condensation. If this interpretation is correct, the apparent lack of induced breakage of premitotic chromosomes is artifactual.     

Studies on the human chromosome 3 centromere with a newly cloned alphoid DNA probe

Starting from a chromosome-specific DNA library, we have isolated a human chromosome-specific satellite DNA sequence. This sequence of 635 base pairs (bp) consists of 3.7 alpha DNA monomers of 170-171 bp. Under high stringency it hybridizes to the centromere of chromosome 3 in a region composed of 2,750 bp tandem repeats characterized by the regular spacing of Hind III and TaqI restriction enzyme recognition sites. It has diverged and undergone amplification after the human speciation. The amplification allows an easy monitoring of the chromosome 3 centromere by in situ hybridization with a nonradioactive probe.     

Chromosome banding and genome compartmentalization in fishes

The diploid chromosome number of the Chinese raccoon dog varies from 54 (no B chromosomes) to 58 (4 B chromosomes). The B chromosomes are totally heterochromatic. An electron microscopic study was made of the synaptonemal complexes (SC) in spermatocytes of these animals. The SC karyotype consists of 27 regular chromosome pairs (autosomes and the sex chromosomes) plus the B chromosomes. The Bs pair effectively with one another at pachytene, but the SC axes of the B chromosomes are much denser than those of the A chromosomes. Depending on the number of Bs, both bivalents and multivalents have been observed. When three B chromosomes are present in a cell, parallel alignment of all three SCs can be seen. Formation of multivalents indicates high homology among these supernumerary heterochromatic chromosomes. Fusiform bulges are found along unpaired regions of all chromosomes which are particularly pronounced in diplotene.     

Diagrammatic representation for chromosomal mutagenesis studies. III. Radiation-induced rearrangements in Pan troglodytes (chimpanzee)

A qualitative study is presented of chromosomal rearrangements induced by gamma-irradiation at 2 Gy and 3 Gy in peripheral blood lymphocytes of the chimpanzee Pan troglodytes. From a sample of 460 cells, karyotyped after R-banding, 1047 rearrangements were detected. Each type of rearrangement is analyzed according to the diagrammatic method previously developed. The non-random nature of the induction of the rearrangements is clear. The chimpanzee seems highly sensitive to the induction of dicentrics. This may be related to the existence, in its karyotype, of sensitive juxta-telomeric heterochromatin, much more frequently affected in the case of formation of dicentrics than of other types of rearrangements. Thus, the evaluation of radiation sensitivity of a given species based only on the yield of dicentrics may not have a general value for chromosomal mutagenesis.     

Detection of 1q polysomy in interphase nuclei of human solid tumors with a biotinylated probe

Summary A biotinylated probe (L23-21) specific for the 1q12 band of human karyotype was used to detect the 1q segment in interphase nuclei of breast and colon carcinomas. This probe was selected because trisomy or polysomy 1q is the most frequent chromosomal change observed in solid tumors. This method enables cancerous cells, including near-diploid ones carrying an unbalanced rearrangement of 1q, to be easily identified.