Crepis capillaris (2n=6) is an excellent plant for the assay of chromosome aberrations after chemical treatment. C. tectorum (2n=8) has been used also in mutagenic studies, but to a much lesser extent. A protocol has been given for using root tips to study the cytological endpoints, such as chromosome breaks and exchanges, which follow the testing of chemicals in somatic cells. Meiotic endpoints have not been used in C. capillaris for testing potential chemical mutagens but should be considered, especially a meiotic micronucleus assay. From a literature survey, 81 chemicals are tabulated that have been assayed in 162 Crepis assays for their clastogenic effects. Of the 162 assays that have been carried out, 40 are reported at giving a positive reaction (i.e., causing chromosome aberrations), 97 positive and with a dose response, 7 borderline positive, and 17 negative. Eighty-five percent of the chemicals gave a definite positive response. Assays for one chemical gave contrary results, and were not included in the above tabulation. The Crepis bioassay has been shown to be an excellent plant bioassay for assessing chromosome damage induced by chemicals and environmental pollutants.
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