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The genetic effects of 85Sr gamma irradiation during the weightless phase of the Biosatellite II mission was studied on survival of asexual spores (conidia) of a twocomponent heterokaryon of Neurospora and the induction of recessive lethal mutations. A series of samples of conidia collected on the surface of "Millipore" filters were irradiated simultaneously in the spacecraft and on the ground. Postflight comparisons showed no significant differences in dose-response curves for (1) survival of heterokaryotic conidia, (2) the induction of recessive lethal mutations throughout the genome and (3) the induction of recessive lethal mutations at the ad-3A and ad-3B loci. Present data from the genetic analysis of the Neurospora experiment on the Biosatellite II mission indicate that there is no effect of space flight alone or in combination with gamma radiation on cellular inactivation or induction of recessive lethal mutations. These data tentatively confirm the results obtained with conidia on Millipore filters in the GeminiXI S-4 Neurospora experiment. The recessive lethal mutations at the ad-3A and ad-3B loci result both from point mutation and multilocus deletion and genetic tests are used to characterize these mutants with regard to genotype, "reparability" and allelic complementation. The results of these tests, which will indicate whether there is any difference in the spectrum of mutation between the flight and ground samples, will be summarized. Research sponsored jointly by the National Aeronautics and Space Administration, and the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation.

EFFECTS OF WEIGHTLESSNESS ON RADIATION-INDUCED INACTIVATION AND MUTATION-INDUCTION IN NEUROSPORA CRASSA