514 RADIATION BIOLOGY 



far as could be determined) comprised more than a third of the body in 

 over 90 per cent of the mosaic male offspring. He also found, in agree- 

 ment with earlier but less definitive observations by MuUer (1928b), that 

 as high a proportion of mosaics was produced when the sperm had been 

 aged in the male for two weeks after exposure as when the males had 

 inseminated the females shortly after treatment. This result, which is 

 contrary to that found by Auerbach (1952) with mustard, indicated that, 

 if there was any aftereffect, it did not tend either to mature or to become 

 counteracted by prolonged aging during the spermatozoon stage. This, 

 in turn, suggests that the apparent aftereffect involved in the production 

 of mosaics consists only in the postponement of union between broken ends 

 which later work showed to be characteristic of the spermatozoon stage. 

 On the other hand, as expected if there was no real mutagenic aftereffect, 

 irradiation of females failed to give rise to mosaics (Timofeeff-Ressovsky, 

 1937a, b; Muller, Valencia, and Valencia, unpublished data), and this also 

 appeared to be true when immature male germ cells were irradiated, both 

 in the work of Timofeeff-Ressovsky (1937a, b) and in that of Neuhaus 

 (1934, 1935). 



When one of the two chromatids derived from an X chromosome 

 irradiated in a spermatozoon has been lost by bridge formation that 

 followed simple chromosome breakage, or has had a large portion deleted 

 by double breakage, the resulting mosaic is a gynandromorph ; if one of 

 these accidents happens to a Y chromosome having a visible marker 

 gene, the mosaic, although all of one sex, may, nevertheless, exhibit the 

 pattern of its mosaicism. Gynandromorphs thus produced have been 

 studied in large numbers and in great detail by Patterson and Stone 

 (1938) and by Bonnier et at (1949). Although the hypoploid portion of 

 the body was found to vary greatly in size and shape, it averaged about a 

 third of the whole body in both sets of observations, and Bonnier believes 

 it to be derived, in the great majority of induced cases, from a half-and- 

 half condition in which the proliferation of the affected nucleus had been 

 somewhat retarded, perhaps by the bridge formation. Mosaics produced 

 by losses of the Y chromosome induced by radiation have not yet been 

 studied on an adecfuate scale, but, at this time, indications are that these 

 mosaics also are usually half-and-half in origin. 



Since losses of the X chromosome may be made much more abundant 

 by irradiating a ring-shaped X chromosome, experiments were carried 

 out by Battacharya (see Muller, 1940; Battacharya, 1950), under the 

 direction of Muller, with the object of ascertaining whether the chromo- 

 some of this kind derived from an irradiated spermatozoon was ever lost 

 after the first few cleavage divisions. For this purpose the nonring X 

 chromosome, supplied by the nonirradiated mother, was caused to con- 

 tain the gene for white eyes, and the eyes of the offspring were carefully 

 examined for the white spots which would indicate the loss of the ring 



