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.