Mosaic mutations induced in Drosophila by ethylenimine.

irst well defined case of the mutagenic effectiveness of chemicals was Tyet:ied for mustard gas treatment of Drosophila by AUERBACH and ROBSON ( 1946). Chemical mutagenesis studies have since been extended to a number of biological systems, including bacteria, fungi and higher organisms. AUERBACH (1965) has discussed the development of chemical mutagenesis in the last 20 years. The application of chemicals in studies of the nature of the gene and of mutagenic processes was related to advances in biochemical knowledge of the gene and the use of new genetic systems. More recently, AUERBACH (1967) presented a review of the history of mutation research. The experimental approaches, theoretical applications and important discoveries in the field of genetic mutagenesis were considered. Also, the different characteristics of mutagenesis and the important problems of mutation research were thoroughly outlined and discussed. The high rate of delayed, genetic mosaic lethals induced by chemicals clearly sets chemicals apart from radiation mutagenesis and indicates some differences in the mutagenic processes following chemical and radiation treatments. With chemicals, mutagenic effectiveness may be continued in the untreated, successive generation (AUERBACH 1945). The presence of delayed mutations after chemical treatment often makes the total effective mutation rate unpredictable, and increases mutational risks to the genetic system. Delayed mutations appear at a higher rate in mature sperm of Drosophila than in other postmeiotic and premeiotic germ cells after ethylenimine treatment (ALEXANDER and GLANGES 1965). A high ratio of mosaics to complete lethals was reported for mature sperm for chloroethyl methanesulphonate treatment by MATHEW (1964). Fairly similar complete and mosaic lethal rates were reported for the first nine days of remating periods (postmeiotic cells) by CARLSON and SOUTHIN (1963) for treatment of Drosophila with ICR-100, (now called ICR-170) (2-methoxy-6-chloro-9 (-3[ethyl-2-chloroethyl] amino-propylamino) acridine dihydrochloride) . In the present study with ethylenimine, delayed, mosaic mutations, along with complete lethals induced in treated chromosomes, were tested in postmeiotic germ cells of Drosophila. The mosaic lethal rates in the X chromosome were tested for two generations after chemical treatment in order to characterize the production of mosaic lethals; this is necessary for determining the mechanisms involved in this particular type of genetic damage.