Genetic and biochemical analysis in microorganisms has been greatly facilitated by the use of conditional lethal mutations that die under "restrictive" conditions but survive in a "permissive" environment." 2 One class of conditional lethals, the temperature-sensitive (ts) mutants that result from a single amino acid substitution that renders a polypeptide inactive at high temperatures,3-5 has been extensively analyzed in Neurospora,6 bacteria,7 T4 phages,"8 and tobacco mosaic virus.3 4 In higher organisms, ts mutants have been detected in Arabidopsis,9 Paramecium,'0 and Drosophila. II The potential usefulness of ts mutants in several types of genetic analyses prompted us to screen for them systematically in Drosophila melanogaster. This paper reports the frequencies of ts mutants among sex-linked recessive lethals and semilethals induced by Py-rays, ethyl methanesulfonate, and mitomycin C. Methods and Materials.-Screening technique: Oregon-R males were collected within 48 hr of eclosion, treated as described below, and then mated separately with three Basc females in vials at room temperature (230 1 20C). The males were transferred without etherization to a fresh set of females at 2-day intervals for several consecutive broods. Each set of females was removed from the vials 3 days after transfer of the males in the experiments with mitomycin C and y-rays. Owing to the poor fertility of males treated with ethyl methanesulfonate, females in these experiments were allowed to lay eggs for up to 5 days after transfer of the males and in some cases were then transferred to a fresh vial. Single F, females from each brood of each male were placed together with one or two Basc males at 290 ± 0.50C. The presence of two or less non-Basc F2 males in a fertile culture suggested that a lethal or semilethal had been induced on the X chromosome. Replicate cultures of the F2 of all possible lethals and semilethals were set at-290C and

No abstract

tivity that the turtle shows for the low tones. Our problem becomes easier if we consider also the other sort of hydraulic factor referred to above, the ratio between the areas of the stapedial footplate and the round window. If we use the value of 8 for this latter ratio as suggested, the total transformer ratio becomes 68, which is close to the figure obtained in the cat. This second factor needs more precise determination, but it appears from this preliminary consideration that the turtle's ear is well adapted to the reception of aerial sounds, at least in the low-frequency range. * This investigation was supported in part by the Office of Naval Research, under Contract N6-onr-270-3, and by Higgins funds allotted to Princeton University. Permission is granted for reproduction and use by the United States Government. 1 E. G. Wever and J. A. Vernon, "The Sensitivity of the Turtle's Ear as Shown by Its Electrical

No abstract

No abstract