10 



BIOLOGIC BASIS OF SEX 



fore and roughly proportional to the quan- 

 titative change in the genie constitution." 



Since the sexually different types ob- 

 served by Bridges were accompanied by 

 whole chromosomal differences, he could 

 point to losses or gains of autosomes, with 

 an internal preponderance of genes tending 

 to develop male organs, as balanced by 

 genes of the X chromosomes tending in the 

 direction of producing female organs or of 

 suppressing alternative male organs. The 

 net effect of the X chromosome favoring fe- 

 maleness, and of the set of autosomes fa- 

 voring maleness, terminates in the devel- 

 opment of male or female, according to the 

 ratio of these determiners in the whole 

 genotype. The effect of the X chromosome 

 goes on the basis of whole numbers 1, 2, 3, 

 4, as does the similar variation in the sets 

 of autosomes. 



Goldschmidt, since he was dealing with 



TABLE LI 



Chromosomal numbers and kinds for the different 



recognized sex types of Drosophila 



Type 



Superfemale . . . 

 Triploid meta- 



female 



Female* 



Female 



Female 



Female 



Female 



Female 



Female 



P'emale 



Female 



Female 



Intersex* 



Intersex 



Intersex 



Male 



Male 



Male 



Male 



Male* 



Supermale 



X/A Balance 



1.5 



L3 



LO 



LO 



LO 



LO 



LO 



1.0 



LO 



LO 



LO 



LO 

 .75 

 . ()7 

 .()7 

 .50 

 .50 

 .50 

 .50 

 .50 

 .33 



* These forms are cited by Bridges from his 

 own observations, from L. V. Morgan (1925) and 

 from Sturtevant (unpublished). As yet but limited 

 studies of these forms, which must be rare, have 

 been published. Fourth chromosomes generally, 

 but not always, equal mimber of the other indi- 

 vidual chromosome gn)U])s. 



males and females of the diploid type, took 

 a corresponding view for the Z chromo- 

 somes of his moths with this difference. 

 Since the Drosophila chromosome pattern 

 is XY + 2A for the males as contrasted to 

 2X + 2A for the females and the pattern 

 for Lymantria is ZZ -|- 2A for the males 

 and ZW + 2A for the females, it was neces- 

 sary to use a relation which was reciprocal 

 to that of Drosophila; the male determining 

 element or elements were assigned to the Z 

 chromosomes. Lymantria has a rather large 

 number of different races found in different 

 geographic locations. Within any one of 

 these races this formulation apparently suf- 

 ficed. However, from crosses between races 

 it was soon observed that the progeny 

 showed ranges in sexuality all the way from 

 phenotypic males to phenotypic females al- 

 though these females were actually genetic 

 males. To Goldschmidt, this variation indi- 

 cated different potencies of the male-deter- 

 mining element. Similar differences were at- 

 tributed to the female element which he 

 had first assigned to the cytoplasm but for 

 which he later favored a W chromosome 

 location. 



In applying this postulate of discrete 

 chromosome contributions to sex according 

 to their number, Bridges made the further 

 assumption that female-producing genes 

 l)redominate in the X and are scattered 

 through it in more or less random fashion 

 as are the genes affecting so-called somatic 

 characteristics as wing shape or bristle pat- 

 tern. The quantitative relations for the dif- 

 ferent chromosomal types, together with 

 their descriptions, are indicated in Table 

 1.1. 



In the formulation of Table 1.1, the X 

 and Y chromosomes are counted separately, 

 whereas a set of A chromosomes (auto- 

 somes), is allowed a value of but one even 

 though comjiosed of a 2nd, a 3rd, and a 

 4th chromosome for the haploid genome. 

 The dii)loid set of autosomes is given a 

 weight of two, and so on. From these data 

 Bridges observed that the presence or ab- 

 sence of a Y chromosome did not affect the 

 sex types. The X chromosomes and auto- 

 somes were, however, important. He held 

 that their importance stood as the ratio of 

 thcii' prcsuiiK'd iM'oducts to each other. The 



