24 



BIOLOGIC BASIS OF SEX 



ondary if not primary sex characteristics. 

 As with many other species it has loci for 

 genes which are also found in the X chro- 

 mosome, i.e., bobbed, as well as a limited 

 number of bands in the salivary gland chro- 

 mosome. Nucleolus organizers and at least 

 two specialized pairing organelles similar 

 to those in the X chromosome are found 

 within the Y chromosome (Cooper, 1952, 

 1959). One of the most significant proper- 

 ties is the effect of extra Y chromosomes on 

 the variegation observed for various gene 

 phenotypes either in the normal chromo- 

 some pattern or in that accompanying 

 translocation. In variegation one Y chro- 

 mosome as extra to the normal complex is 

 sufficient to eliminate or more rarely to 

 much reduce the variegated expression 

 (Gowen and Gay, 1933). When the Y chro- 

 mosomes are 2 above the normal comple- 

 ment, the phenotypes gain two new features 

 (Cooper, 1956). Both males and females 

 become variegated in the expression of their 

 eye characteristics. The males become ster- 

 ile. These effects are unexpected for they 

 are counter to any previous trends in the Y 

 effects on these characteristics. They have 

 reversed the direction of the effects as es- 

 tablished by the two previous chromosome 

 types. The variegation of the XX2Y + 2A 

 females and X3Y + 2A males resembles 

 that of the XX + 2A females and XY + 

 2A males but is more extreme, whereas the 

 XXY + 2A and X2Y + 2A are largely 

 nonvariegated. The fertility relations are 

 equally aberrant: the X3Y + 2A males 

 have the same type sterility through loss of 

 sperm motility as that of the XO + 2A 

 males. Bundles of sperm are formed but 

 they do not become motile. Full-sized Y 

 chromosomes are not required to bring 

 about these effects, because females having 

 a whole Y plus a piece of a second, or males 

 with 2Y plus a piece of a third, will show 

 the effects. 



The fractional Y chromosomes furnish 

 opportunities to test for the partial inde- 

 pendence of the variegation and sterility ef- 

 fects. The two Y hyperploid males differ in 

 their degree of fertility according to the 

 fraction of the Y chromosome which may 

 be present whereas the effects on variega- 

 tion may be constant among groups. This is 

 in accord with the sterility l)eing in part 



independent of the factors causing the var- 

 iegations. Similarly, the variegations may 

 be shown to be partially free of the action 

 of some elements that are not themselves 

 members of the two sets of factors influ- 

 encing fertility in the normal male. 



Other phenotypic irregularities appear; 

 eye facets may be roughened, legs short- 

 ened, and wing membranes become abnor- 

 mal. On the negative side two extra Y chro- 

 mosomes in females homozygous for the 

 transformer gene, tra, do not increase in 

 maleness or function. 



The variegations of the so-called V-type 

 position effects with translocations are sup- 

 pressed, as in the normal type described, 

 by one extra Y but are nonetheless vari- 

 egated when two extra Y chromosomes are 

 present. That these effects are caused by 

 there being two supernumerary Y's is in- 

 dicated by the fact that XX2Y females are 

 fertile and X3Y males sometimes lose a Y 

 chromosome in their germinal tracts and 

 become fertile. A number of mechanisms 

 have been suggested to account for these 

 results but most have proven unsatisfac- 

 tory. A balance interpretation for the X, Y 

 and autosomes like that for sex, as sug- 

 gested by Cooper (1956) is compatible with 

 the somatic cell variegations for euchro- 

 matic loci transferred to the heterochro- 

 matic regions and the sterility-fertility 

 relations expressed by the different chromo- 

 somal types. 



The variegation effects of the Y chromo- 

 some take on further significance. Baker 

 and Spofford (1959) have shown that 15 

 different fragments of the Y chromosome 

 when studied for their contributions to var- 

 iegation differ in their effects with the dif- 

 ferences often not related to the size of the 

 fragment, thus indicating that the Y chro- 

 mosome has linearly differentiated factors 

 capable of modifying the variegated pheno- 

 type. 



Other indications of genetic activity of 

 the Y chromosome were given by Aronson 

 (1959) in her study of the segregation ob- 

 served in 3rd chromosome translocations. A 

 deficiency for the region of the 3rd chromo- 

 some centromere is lethal when homozy- 

 gous. Both males and females are fully 

 \'iable when this deficiency is heterozygous. 

 XO or haplo IV deficient males die. How- 



