Sixty first instar larvae were placed in each of the eight flight modules. Ten first instar larvae with ring chromosomes were selected for cytologic preparations. Additional larvae were added to bring the count to 290. After flight the larvae were examined for visual chromosome changes and some were allowed to develop and breed. The larvae were exposed to a dose of 1,200 to 1,500 r of 85Sr; one unit was shielded. A similar configuration was used on ground controls, with three additional controls being maintained. One important aspect of this experiment was the incorporation of a ring-shaped X chromosome into some of the strands used. In experimental conditions, ring chromosomes can persist as stable entities until subject to breakage, serving to greatly amplify the sensitivity of this system.

Results:

Although radiation did increase somatic and reproductive cell mortality, it did so irrespective of whether the larvae had been subject to the particular conditions present during flight (including weightlessness). However, a higher mortality of orbited larvae than ground radiation-exposed larvae was noted with no detectable difference in developmental time. Chromosomes flown and irradiated showed a statistically significant increase in chromosome change over controls. Sex- linked recessive lethals and crossing over were enhanced when the radiation was delivered under conditions of weightlessness. Data suggest that radiation interacts with weightlessness to induce more premature aging and chromosome damage in actively growing and metabolizing specimens than in those irradiated on Earth. Possibly some factor, more than likely weightlessness, is capable of causing improper chromosome separation and formation of chromosome translations.