Comparative mutagenesis of the dumpy locus in Drosophila melanogaster. II. Mutational mosaicism induced without apparent breakage by a monofunctional alkylating agent.

Abstract

Monofunctional quinacrine mustard (ICR 100) induces mutations at the dumpy locus with an average frequency of 0.88%. More than 90% of the recovered dumpy mutations are distributed mosaically in somatic and gonadal tissues. Mutation frequencies at 16 other loci expressing visible effects were low or negligible. These experiments suggest that x-ray-induced mosaic mutations become established primarily at the first synchronous nuclear division of the zygote and that the ICR 100-induced mosaic mutations become established primarily at a later replication. Sex linked lethals scored in the F/sub 2/ occur with a frequency of 3.7%; mosaic sex-linked lethals detected by scoring in the F/sub 3/ occur with a frequency of 13.7%. The mutational spectrum of the dumpy alleles induced by x rays does not differ appreciably from that induced by the ICR 100. ICR 100 is capable of inducing mutations in spermatozoa, spermatids, and the earlier stages of meiosis, including spermatogonia. No evidence for breakage everts at the dumpy locus was detected in the progeny derived from ICR 100-treated sperm. The use of the sex-linked lethal test as ordinarily applied, i.e. by examination only of the F/sub 2/ generation, for determining the effectiveness of a chemical mutagen or for equating an equivalentmore » roentgen dose to various conceatrations of chemical mutagen can be misleading. However, the test can be made more meaningful by continuing the analysis for another generation and/or combining it with a test for visible mutations at specific loci. (auth)« less