498 The Determination of Sex 



the other hand, this condition could also result from a nondis- 

 junction of an X chromosome resulting in some XO cells and 

 other cells which would be XXX. In such a gynander part of 

 the body would be male and the remainder would be super- 

 female. The actual chromosomal situation has not been con- 

 firmed by visual observations of the chromosomes, and, as super- 

 female tissue is not easy to differentiate from normal female 

 tissue, it may well be that at least some of the gynanders are 

 XO in one part of their body and XXX in the other. It is pos- 

 sible also that gynanders may result not from the loss of a com- 

 plete X chromosome but merely from a deletion (or inactiva- 

 tion) of the female-determining genes in one of the X chromo- 

 somes. In such gynanders, however, the male region would 

 not show the loss of any sex-linked genes unless they happened 

 to be in the deleted region. 



In gynanders, the extent of the male tissue will depend upon 

 the particular cell division at which the X chromosome was 

 eliminated and, of course, upon cell lineage, which may be 

 variable. If chromosome elimination occurred during the di- 

 vision of the zygote, half the body would be male and half 

 female; but if it occurred during some subsequent division the 

 amount of male tissue would be less. In all gynanders, however, 

 it is probable that the individual started out as a female. These 

 flies often cannot function as either sex because of the abnormal 

 condition of their sex organs but some gynanders are fertile, hav- 

 ing sex organs of one type only. 



Habrobracon 



Gynandromorphs have thrown some light on the determina- 

 tion of sex in the parasitic wasp, Habrobracon juglandis. The 

 females in this species are diploid and the males are hap- 

 loid, but inbreeding always produces diploid males which are 

 highly sterile unless selection against them is very rigid. Sex 

 appears to be determined largely by the presence of different 

 alleles of the sex factor which is present as a series of multiple 

 alleles, xa, xb, xc, etc. The rules for the formulation of genetic 

 symbols indicate that superscripts should be used for multiple 

 alleles, in which case the symbols here should be x'^, x^ x'^, etc. 

 However, the other symbols have been used for a number of years 

 by the workers with Habrobracon and will be used here. 



