Effect of Ziram, Thiram, and Dithane M-45 on bone marrow cells of mice-assessed by micronucleus test.

Micronucleus test is an extensively used protocol to assess the mutagenicity of environmental chemicals. This was developed by Schmid and his co-workers (Matter and Schmid, 1971; Ledebur and Schmid, 1973). The micronucleus test is simple, quick and as sensitive as the chromosome aberration analysis. It is based on the principle that during anaphase, acentric chromatid and chromosome fragments lag behind, where as centric elements move towards the spindle pole. After telophase both the undamaged chromosomes and the centric fragments give rise to the daughter nuclei. The lagging elements are transferred into one or several secondary nuclei, which are as a rule much smaller than the main nucleus, and therefore called micronucleus (Schmid, 1973). The clastogenic effect of various chemicals is measured by micronucleus test. Erythrocytes are two types, the younger ones are polychromatic erythrocytes (PCE), which stain bluish and the older, the normo chromatic erythrocytes (NCE) which stain reddish. A few hours after the completion of last mitosis the erythroblasts expel their nucleus for unknown reasons and the micronucleus alone remains in the cytoplasm of the Polychromatic erythrocytes, and they are easily recognisable. Erythrocyte micronucleus represents the consequence of chromosomal aberrations induced during preceding mitotic division of erythrocytes (Matter and Grauwiler, 1974).