26 



BIOLOGIC BASIS OF SEX 



fail to appear, in some instances fail to 

 transmit the condition or produce inter- 

 mediate progeny ratios, as well as in some 

 instances to skip a generation. The infec- 

 tious agent was found to vary in different 

 species. Magni (1953, 1954) for D. bi- 

 fasciata found that temperature above nor- 

 mal tended to remove the cytoplasmic agent 

 making it ineffective. This result has a par- 

 allel to the action of temperature on certain 

 viruses, as for instance that involved in one 

 of the peach tree diseases. On the other 

 hand, Malogolowkin (1958) ior D . willistoni 

 found no temperature effect. Malogolowkin 

 further found that the cytoplasmic factor 

 was not independent of chromosomal genes 

 since some wildtype mutant strains induced 

 reversions to normal sex ratio. Recently 

 Poulson has established the complete corre- 

 lation of the high female progeny character- 

 istic with the presence of a Trepomena in 

 the fly's lymph. As with mouse typhoid vari- 

 ations, lethality was genotype dependent. 



These cases have interest from more than 

 the sex ratio viewpoint. Cytoplasmically 

 inherited susceptibility of some strains of 

 D. 7nelanogaster to poisoning by carbon di- 

 oxide as studied by L'Heritier (1951, 1955) 

 depended on the presence of some cyto- 

 plasmic entity which passed through the egg 

 cytoplasm and also, but less efficiently, by 

 means of the male sex cells to the progeny. 

 The carbon dioxide susceptibility was trans- 

 mitted through injections of hemolymph or 

 transplantation of organs of susceptible 

 strains. The transmissible substance had a 

 further property of heat susceptibility. The 

 COo susceptibility differed from that of "sex 

 ratio" in being partially male transmitted. 

 It agrees with ''sex ratio" D. bifasciata in 

 being heat susceptible but differs from D. 

 willistoni "sex ratio" in this respect. 



D. bifasciata may behave differently than 

 D. willistoni in that Rasmussen (1957) and 

 Moriwaki and Kitagawa (1957) both con- 

 ducted transplantation experiments with 

 negative results. However, it is jiossible that 

 these experiments may be affected by a 

 different incubation period for the injected 

 material as contrasted with that for D. 

 willistoni. A range of possibilities evidently 

 exist for extrinsic effects in sex ratio. 



Carson (1956) found a female producing 

 strain of D. borealis Patterson, which car- 



ried on for a period of 8 generations, pro- 

 duced 1327 females with no males. The 

 strain showed no chromosomal abnormali- 

 ties. It had 3 inversions. The females would 

 not produce young unless mated to males 

 from other strains having biparental in- 

 heritance. This requirement, together with 

 gene evidence, showing that the females 

 were of biparental origin, is against the fe- 

 male progenies being derived by thelytokous 

 reproduction. 



F. MALE-INFLUENCED TYPE OF 

 FEMALE SEX RATIO 



Sturtevant in 1925 described exj^eriments 

 with a stock of D. affinis in which a great 

 deficiency of sons was obtained from certain 

 males, regardless of the source of females 

 to which such males were mated. The few 

 males obtained from such matings were nor- 

 mal in behavior but some of the sons of 

 females from such anomalous cultures again 

 gave very few sons (]Morgan, Bridges and 

 Sturtevant, 1925). 



Gershenson (1928) in a sampling of 19 

 females caught in nature found two that 

 were heterozygous for a factor causing 

 strong deviations toward females (96 per 

 cent to 4 per cent males) whereas the nor- 

 mal D. pseudoobscura ratio was nearly 1 to 

 1. The factor was localized in the X chromo- 

 some and was transmitted like an ordinary 

 sex-linked gene. Its effect was sex limited 

 as it was not manifest in either hetero- 

 zygous or homozygous females. It had no 

 effect on the development of zygotes al- 

 ready formed but strongly influenced the 

 mechanism of sex determination through the 

 almost total removal of the spermatozoa 

 with the Y chromosome from the fertiliza- 

 tion process. Egg counts showed the di- 

 vergent ratio toward females was not caused 

 by death of the male zygotes inasmuch as 

 there was no greater mortality from such 

 cultures than from controls giving 1 to 1 sex 

 ratios. 



Sturtevant and Dobzhansky (1936) 

 showed that an identical or nearly identical 

 phenotypc to that obscM'ved in Drosophila 

 obscura was present in D. pseudoobscura. 

 The D. pseudoobscura carrying the factor 

 were scattered over rather wide geographi- 

 cal areas. Comparable types also were found 

 in two other species D. athabasca and D. 



