Homozygous diploid zebra fish have been produced on a large scale by the application of simple physical treatments. Clones of homozygous fish have been produced from individual homozygotes. These clones and associated genetic methods will facilitate genetic analyses of this vertebrate.

Production of clones of homozygous diploid zebra fish ( Brachydanio rerio )

Short-term tests for carcinogens and mutagens

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Sister-chromatid exchanges: a report of the GENE-TOX program.

EARLY RESULTS                                                        1 83 Sister Chromatid Exchange in Meiosis 1 83 Sister Chromatid Exchange in Somatic Cells 1 84 Isolabeling 1 86 Sister Chromatid Exchanges-Spontaneous or Induced? 1 86 RESULTS FROM NEW METHODS FOR DETECTING SISTER CHROMA TID EXCHANGES                  1 86 Reasons for Differential Staining                   1 87 Harlequin Chromosomes and Chromosome Structure     1 89 Multiple sister chromatid exchanges 1 90 Autoradiographic image spread            1 90 Labeling for more than one replication cycle           1 90 The Question 0/ Spontaneous Levels 0/ Sister Chromatid Exchanges      1 9 1 Location 0/ Sister Chromosome Exchanges in the Chromosome      1 93 Sister Chromatid Exchanges and Human Genetic Diseases      1 93 Sister Chromatid Exchanges as Indicators 0/ Mutagenic Carcinogens         1 94 Lesions Responsible for Sister Chromatid Exchange Formation      1 96 CONCLUSION                                                                                                                   1 97

Sister Chromatid Exchange

Diverse plant and animal species have B chromosomes, also known as accessory, extra or supernumerary chromosomes. Despite being widely distributed among different taxa, the genomic nature and genetic behavior of B chromosomes are still poorly understood. In this study we describe the occurrence of B chromosomes in the African cichlid fish Haplochromis obliquidens. One or two large B chromosome(s) occurring in 39.6% of the analyzed individuals (both male and female) were identified. To better characterize the karyotype and assess the nature of the B chromosomes, fluorescence in situ hybridization (FISH) was performed using probes for telomeric DNA repeats, 18S and 5S rRNA genes, SATA centromeric satellites, and bacterial artificial chromosomes (BACs) enriched in repeated DNA sequences. The B chromosomes are enriched in repeated DNAs, especially non-active 18S rRNA gene-like sequences. Our results suggest that the B chromosome could have originated from rDNA bearing subtelo/acrocentric A chromosomes through formation of an isochromosome, or by accumulation of repeated DNAs and rRNA gene-like sequences in a small proto-B chromosome derived from the A complement.

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The B chromosomes of the African cichlid fish Haplochromis obliquidens harbour 18S rRNA gene copies.

A technique is described for obtaining well-spread metaphases from solid tissues of fishes without the use of methodologies that rely on tissue grinders, centrifuges, digestive enzymes, or tissue culture. This procedure involves the formation of a cell suspension from acetic alcohol fixed tissues using 50% acetic acid. The suspension is applied to a warm (50 °C) slide using a micropipette.Solid tissue preparations may be stained by any of the conventional dyes or treated to reveal Q-bands, C-bands, and nucleolar organizers. Large numbers of slides offish chromosomes can be made easily and rapidly using this procedure.

Rapid Chromosome Preparations from Solid Tissues of Fishes

Sister-chromatid exchange (SCE) studies using the central mudminnow, Umbra limi, demonstrated its usefulness as a model in vivo system for the detection of genetically active substances (mutagens and/or carcinogens). 5 days following the injection of 500 μg/g of 5-bromodeoxyuridine (BrdU), SCE rates were found to be quite low in the gills (2.0–3.3 SCEs/metaphase), kidneys (2.6–3.4 SCEs/metaphase), and intestines (3.7–4.5 SCEs/metaphase). However, after i.p. exposure to microgram quantities of methyl methanesulfonate (MMS) or cyclophosphamide (CP), large linear dose-dependent increases in SCE rates were observed in all tissues examined. On a μg/g basis, CP was found to be a 2–4 times more potent inducer of SCE than was MMS. Studies involving the addition of neutral red dye (NR) to the fish's aquarium water revealed that the mudminnow could concentrate the due in its gill and kidney tissues. This dye was found to cause significant increases in SCE rates at water levels of less than 0.1 ppm. However, the concentration of dye in the tissues did not show a correlation with the SCE rate. Possible explanations for this observation are presented in the text. These findings demonstrate the feasibility of using a fish such as the mudminnow to investigate cytogenetic consequences of aquatic pollution.

Induction of sister chromatid exchanges in the central mudminnow following in vivo exposure to mutagenic agents

An in vivo system for the detection of sister chromatid exchange (SCE) in the central mudminnow, Umbra limi, is presented. Sister chromatid differential (SCD) and SCE were demonstrated by fluorescent and Giemsa procedures 5 to 6 days after the fish were injected with 500 mug/g of BrdU. The exchange rate was found to be 2.64 SCEs metaphase in the intestines and 2.42 SCEs/metaphase in the gills. SCE analysis in U. limi should be a useful tool for measuring the mutagenicity of water-borne chemicals.

Andrew D. Kligerman

Papers

Rapid Chromosome Preparations from Solid Tissues of Fishes

Induction of sister chromatid exchanges in the central mudminnow following in vivo exposure to mutagenic agents

Sister chromatid differentiation and exchanges in adult mudminnows (Umbra limi) after in vivo exposure to 5-bromodeoxyuridine