Intersexes in Lymantria 483 



but only two sets of autosomes. These aneuploids have a ratio 

 of 1.5 : 1 and are females but have poor viability and are highly 

 sterile. Thus, the higher the ratio of X chromosomes to auto- 

 somes, the greater the tendency towards femaleness. 



That the Y chromosome does not determine maleness in Dro- 

 sophila is also shown in flies in which this chromosome had be- 

 come lost as the result of a meiotic abnormality. Such flies have 

 one X chromosome and two sets of autosomes but are typical 

 males. They are sterile, however, but this is another matter. 

 Although the Y chromosome does not have an effect on sex de- 

 termination it does contain genes for male fertility which are 

 necessary for the production of a fertile male. That the Y chro- 

 mosome is not the determining factor in sex is further supported 

 by aberrant diploid individuals such as the attached-X type in 

 which two sets of autosomes, two X chromosomes, and one Y 

 chromosome are present. These individuals are females in spite 

 of the presence of the Y chromosome. Thus the absence of a 

 Y chromosome does not prevent a fly from being a male whereas 

 the presence of a Y does not cause a fly to be a male. 



Although the ratio of X chromosomes to autosomes is oper- 

 ative in determining sex in Drosophila mekinog aster, it is not a 

 universal mechanism. Kosswig has shown that in Platypoecilus 

 xiphidium, a fish, the determining factor is the ratio of the auto- 

 somes to the Y chromosomes, and later in this chapter we discuss 

 at length the plant Lychnis [Melandrium) dioica, in which the 

 female-tendency genes are in the X chromosome and the male- 

 tendency genes in the Y chromosome. 



Intersexes in Lymantria 



A number of intersexes of different grades have been found 

 in crosses between different geographical races of the Gypsy 

 moth, Lymantria dispar. They range from normal males through 

 various stages of low intersexuality and high intersexuality to 

 females which are genetically males but have undergone a sex 

 reversal, or from normal females through all grades of intersexes 

 to males which are genetically females. These intersexes have 

 formed the basis of Goldschmidt's quantitative theory of sex 

 determination. In Lymantria the females are the heterogametic 

 individuals so that, according to the notation we have adopted in 

 this book, the females would be ZW and the males ZZ. In 



