P32-INDUCED LETHAL MUTATIONS IN DROSOPHILA

Abstract

X-chromosomes of P32-treated wild-type Drosophila melanogaster were tested for the presence of recessive lethal mutations. Treated larvae were reared in food medium containing initially 6.5, 32.5, 65.0, or 162.5 mrd. P32 per ml. Of 838 tested chromosomes 42 had recessive lethals. The frequency of mutation was roughly proportional to P32 content of the food. An initial concentration of 18.8 mrd. P32 in larval food is expected to produce about the same frequency of recessive lethal mutations as is obtained with 1000 r. of X rays applied to mature sperm. A fly reared in medium having an initial concentration of 32.5 mrd. per ml. receives, prior to mating, a calculated total radiation dose of 0.62 gram roentgens. At this dosage 4.2% recessive lethals were recorded. For equivalent amounts of ionization P32 is here apparently 2.3 times as effective as X rays.