Nitrogen-treatment Effects on Rearrangement-induction Patterns inDrosophila Melanogaster

Abstract

Recovered rates of Y-chromosome-autosomal translocations (Y-A) induced in spermatids of pupae of Drosophila melanogaster, as well as the chromosomes 2–3 translocations (2–3), were higher in crosses to females having an attached X.Y-chromosome than to regular females. This suggests that numerous position-effect sterility mutations were induced in the Y-chromosome as well as in the autosomes. Nitrogen treatment after irradiation of 800 r did not increase the frequencies of translocations recovered. Prolonged nitrogen pre-treatment apparently retarded development so that irradiation involved an earlier and more sensitive stage of spermiogenesis than without pre-treatment. The increase of the 2–3, was higher than that of the Y-A translocations, indicating a lower stage-sensitivity of the latter. When two irradiations were given 14 hours apart in air, breaks induced in the first irradiation rejoined prior to the second. Prolonged nitrogen treatment after the first irradiation caused a delay in rejoining of most breaks involved in 2–3 translocations, while rejoining of those involved in Y-A translocations was not delayed to a large extent. The sensitivity differences in recovery of Y-A and 2–3 translocations are perhaps a reflection of different rejoining characteristics of heterochromatic and euchromatic breaks. The change in the frequency of X-chromosome recessive lethals over the 14 hours separating the two irradiations applied to the spermatids is much larger than that of breaks involved in translocations. This indicates that at least some recessive lethals are caused by intra-genic mutations as opposed to inter-genic breaks.