FREQUENCY OF SPONTANEOUS MUTATIONS IN CERTAIN STOCKS OF DROSOPHILA MELANOGASTER

Abstract

URING the investigations dealing with various problems in which D the frequency of X chromosome lethals was measured, an unusually high frequency of spontaneous lethals was noticed in the inbred Florida stock. This marked the beginning of an attempt to ascertain the rate of spontaneous mutability in various wild type stocks. The results of these studies will be reported in the present paper. A preliminary account was presented a t the 1936 summer meeting of the Genetics Society of America (DEMEREC 1937a). At the same meeting PLOUGH and HOLTHAUSEN (1937) reported a high frequency of visible mutants in crosses where the Florida stock was used. METHODS The major part of the experiment deals with the determination of the rate of occurrence of spontaneous X chromosome lethals. Throughout this work a uniform procedure was used. Lethals were detected by the CIB method according to the following scheme: (I) CIB/ec ct v g 9 by + 3 (2) F1 GIB/+ 9 by ec ct v g 3 (3) Females from a culture without males were bred as follows: Flies for (I) were raised in 2 pint milk bottles, for (2) in 25x95 mm vials and (3) in $ pint milk bottles. In all cases corn-meal, molasses, and agar food was used, brewers' yeast having been added to make it richer; The food contained about 0.10 percent of Moldex-A. +(Z)/ec ct v g by y Hw, In dl-49. RESULTS Results of experimental tests of fifteen wildltype stocks are summarized in table I. These stocks, obtained from various laboratories, came from places so widely separated geographically that they could be only dis-tantly related. The data show that three of them, Florida-inbred; Wooster, 0.; and Formosa, Japan, have a significantly higher mutability rate than the other twelve stocks tested. Comparing the high mutability stocks with the low mutability Oregon-R, it was found that the Formosa stock has a mutability rate about five times as high as that of the Oregon-R, while Wooster showed a mutability rate about ten times and Florida almost twenty times as high as that of the Oregon stock. GENETICS ta: 469 Sept. 1937