Differential Response of Meiotic Stages in Habrobracon Eggs to Nitrogen Mustard.

N some respects, the mutagenic action of the mustards on Drosophila resembles I that of X-rays. Both are nonspecific in their effects (AUERBACH and ROBSON 1946), each induces an approximate five-to-one ratio of recessive lethals to visible deletions (SLYZINSKA and SLYZINSKI 1947), the same stage of spermatogenesis appears to be sensitive to both mutagens (AUERBACH 1953) and breaks are induced a t random by them on the chromosome limbs (KAUPMANN et al. 1949). Differences in action are also apparent--e.g., X-rays induce a higher proportion of gross rearrangements (AUERBACH 1950), genetic mosaics appear more frequently after mustard exposure (AUERBACH 1950), and KAUFMANN et al. (1949) showed that the number of translocations increases in sperm chromosomes a week or two after exposure to mustard (X-irradiation data show no such increase). It has been conclusively demonstrated in Habrobracon (WHITING 1945a and b), in Sciara (BOZEMAN and METZ 1949), and in Trillium (SPARROW 1948) that contracted meiotic chromosomes in diakinesis, metaphase, and anaphase, are much more sensitive to X-rays than are the more dispersed and relatively immobile prophase chromosomes. In preliminary reports WHITING and VON BORSTEL (1952) and VON BORSTEL (1952) described the action of nitrogen mustard on the oocytes of the parasitic wasp Habrobracon juglandis Ashmead. This study is a continuation of that research and is concerned with induced egg lethality and chromosome breakage. The results demonstrate that nitrogen mustard acts like X-rays in that oocytes in the first meiotic metaphase are much more sensitive to these mutagens than are oocytes in the first meiotic prophase. Furthermore, the study indicates that nitrogen mustard differs from X-rays since single chromatid breaks predominate among the aberrations induced by the former whereas isochromatid breaks predominate among the latter (WHITING 1945b).