Experiments with Drosophila on board the spacecraft Zond-5

A container with 257 eggs of Drosophila melanogaster of the D-32 line, which is characterized by a very low spontaneous mutability, was placed on board Zond-5. The results of two tests on the frequency of lethal recessive point mutations: a) sex-linked and b) autosomal (in the second chromosome) were studied. A significant increase in the frequency of lethals in the X-chromosome of males, presumably caused by the influence of earth conditions after the return of the spacecraft, was found. No substantial increase of such mutations in the X-chromosome of females was found, but a substantial increase in the frequency of autosomal recessive lethals was discovered. Possible explanations of the causes of these events are discussed.