FOUNDATIONS FOR SEX 



25 



ever, in the presence of a Y chromosome the 

 deficient haplo IV males become viable. 

 The lability of this last class indicates that 

 the Y chromosome is genetically active, can 

 compensate for the autosomal deficiency, 

 and thus alter the progeny sex ratio. 



In D. virilis the situation is somewhat 

 different from that observed by Cooper in 

 1956 in D. melanogaster. Baker (1956) has 

 shown that, in a translocation, males having 

 two Y chromosomes plus a Y marked with 

 a 5th chromosome peach are fertile. These 

 results seem to indicate a species difference 

 in the effect of the extra Y on fertility or 

 the Y with the inserted peach locus is not 

 a complete Y and in consequence the true 

 composition of these males is X + 2Y plus 

 a fragment of the Y. The X chromosomal 

 associations in the multichromosomal types 

 are shown to be by trivalents or by tetra- 

 valents. The segregation data indicate that 

 the pattern of disjunction of trivalents is a 

 function of the particular Y chromosome 

 involved. In X2Y males with normal Y's or 

 with one normal and one marked Y, the Y's 

 disjoin almost twice as frequently as they 

 do from trivalents with two identical Y's. 

 Tetravalent segregation is almost entirely 

 two by two, with no preference for any of 

 the three types of disjunction. 



An odd situation was reported by Toku- 

 naga (1958) in substrains of Aphiochaeta 

 .vanthina Speiser. When a male of the sub- 

 strain was crossed to individuals bearing 

 3rd chromosome genes of the original 

 strains, the mutant genes for brown, and so 

 on, behaved as if they were partially sex- 

 linked in the following generations. On the 

 other hand, when a female carrying the par- 

 tially sex-linked genes on the X and Y 

 chromosomes. Abrupt or Occhi chiari, was 

 crossed to the male of the substrain the 

 characters segregated as though they were 

 autosomal. As a working hypothesis it was 

 suggested that in this species the Y chro- 

 mosome had the major male determining 

 factors. The "special" male arose as a trans- 

 location of these factors to the third chromo- 

 some with the consequent change in linkage 

 relations. Data on the role of the X chromo- 

 some in sex determination in this species 

 have not yet been obtained but if they sup- 

 port the interpretation they indicate real 

 differences between this species and that of 



Drosopliila in the location of the sex genes. 

 The results are reminiscent of those ob- 

 tained by Winge in Lebistes as well as those 

 in Melandrium and other forms in which 

 the Y or W chromosomes may contain 

 strong sex genes for either sex. They would 

 further support the thesis that sex genes 

 may be distributed to almost any loci within 

 the inheritance complex. 



E. M.\TERNAL INFLUENCES ON SEX RATIO 



Aside from chance and specific genetic 

 factors, sex ratio is subject to effects from 

 agents intrinsic in the cells of the mothers 

 (Buzzati-Traverso, 1941; Magni, 1952). 

 Strains of Drosophila bifasciata (Magni, 

 1952, 1953, 1957), D. prosaltans (Caval- 

 canti and Falcao, 1954), D. willistoni and 

 D. paulistorum Spassky, 1956 have been 

 isolated which were nearly all of the female 

 sex even though the mothers were outbred 

 to other strains having normal ratio bisexual 

 progeny. Study of these strains by the above 

 workers and Malogolowkin (1958) IVIalo- 

 golowkin and Poulson (1957), and Malo- 

 golowkin, Poulson and Wright (1959), as 

 well as by Carson (1956) have shown in- 

 heritance strictly through the mother re- 

 gardless of the genetic nature of the males 

 to which they were bred. The unbalanced 

 ratio was retained even when the original 

 chromosomes had been replaced by homolo- 

 gous genomes from lines giving normal male 

 and female progenies. Transmission of this 

 unbalanced sex ratio was through the cyto- 

 plasm. Eggs fertilized by Y-bearing sperm 

 died early in the course of development. 

 Malogolowkin, Poulson and Wright (19591 

 have shown that the high female ratio and 

 embryonic male deaths may be transferred 

 from affected females to those which do not 

 normally show the condition through in- 

 jection of ooplasm from infected females. 

 Ooplasm of this same type is, w^hen injected 

 into males, suflficient to cause death to oc- 

 cur within 3 days. In the females a latent 

 period of 10 to 14 days after ooplasm injec- 

 tion was apparently necessary to establish 

 egg sensitization. Once established the con- 

 dition could be transmitted through the 

 female line for several generations. The 

 ooplasm injections were not as efficient in 

 establishing these lines as females found 

 naturally infected. Unisexual broods may 



