September 16, 1921] 



SCIENCE 



253 



The third-chromosome recessive " white-ocelli " 

 had been present in the original culture; and 

 tests of the flies produced by that culture 

 showed that white-ocelli was being distributed 

 in the same abnormal fashion as were plexus 

 brown and speck. Not only were the second- 

 and third-chromosomes involved, but the X- 

 ehromosome as well, as was shown by specific 

 tests with sex-linked characters. 



The hypothesis that the intersexes were 

 triploid was easily put to test by direct cyto- 

 logical examination. The chromosomes (which 

 were unusually clear and well separated) con- 

 sisted of two sets of three Vs (the two sets 

 differing in the size of the Vs), a pair of rods, 

 three or two small round chromosomes, and a 

 J-shaped chromosome or not. That is, all 

 intersexes possessed the second- and the third- 

 chromosomes in triplicate and the X- in dupli- 

 cate, but they might possess three or two 

 fourth-chromosomes, and have or lack a Y- 

 chromosome, so that four sub-types of intersex 

 constitution were found. 



About ten per cent, of the daughters from 

 the original culture, when tested, produced in 

 turn intersexes and further disturbances of the 

 linkage ratios. These females were presum- 

 ably triploid for all the chromosomes (except 

 the fourth, which might be present in dupli- 

 cate) . It was then discovered that these inter- 

 sex-producing females could be identified by 

 their somatic characters, which were similar 

 to, but less extreme than, those of the inter- 

 sexes — namely, large size, coarse bristles, and 

 large roughish eyes. Stocks producing trip- 

 loids and intersexes were maintained more 

 easily by taking advaiitage of the fact that 

 triploid females carrying two white and one 

 eosin gene have a pale yellow eye-color 

 lighter than that of their diploid white-eosin 

 sisters, and likewise that the third-chromosome 

 dominant Delta is dominant over two reces- 

 sive non-Delta genes, but the triploid hetero- 

 zygote is markedly different from the diploid 

 heterozygote. 



With material from thesis stocks genetical 

 proof was obtained that the iutersex-producing 

 females possess in triplicate the loci for a 

 large variety of first-, second- and third-chro- 



mosome genes, and that they might possess 

 fourth-chromosome loci in triplicate or in 

 duplicate. This genetical fitnding, checked by 

 cytological examination, extends the direct 

 proof of the chromosome theory of heredity 

 to specific second- and third-group mutant 

 characters and specific V-shaped chromosomes. 

 Such direct proof had already been provided 

 for certain sex-linked mutants and the rod- 

 shaped chromosomes by the phenomena of non- 

 disjunction of the X-chromosomes,- and more 

 recently for the small round chromosome and 

 the mutants of the " fourth " group through 

 study of " Diminished " individuals haploid 

 for that chromosome because of non-disjunc- 

 tion.^ 



In the triploid strain individuals triploid 

 for the fourth-chromosome alone have been 

 identified as a distinct somatic type, tested 

 genetically in a variety of ways, and proved 

 to be such by direct cytological examination. 



A significant new conclusion proved by the 

 intersexes is that sex in D. nielanogaster is 

 determined by a balance between the genes 

 contained in the X-chromosome and those con- 

 tained in the autosomes. It is not the simple 

 possession of two X-chromosomes that makes 

 a female, and of one that makes a male. A 

 preponderance of genes that are in the auto- 

 somes tend toward the production of male 

 characters; and the net effect of genes in the 

 X is a tendency to the production of female 

 characters. The ratio of 2X : 2 sets auto- 

 somes, or 3X : 3 sets autosomes (or IX : 1 

 set autosome?) produces a female, while IX : 2 

 sets autosomes produces a male. An inter- 

 mediate ratio, 2X : 3 sets autosomes, produces 

 an intermediate condition — the intersex. The 

 fourth-chromosome seems to have a dispro- 

 portionately large share of the total male- 

 producing genes ; for there are indications that 

 the triplo-fourth intersexes are preponderantly 

 of the " male-type," while the diplo-f ourth 

 intersexes are mainly " female-type." 



The condition SX: 2 sets autosomes should 

 be " super-females," and IX : 3 sets autosomes 

 " super-males." Triploid females produce a 



2 Genetics, 1, 1916. 



3 In press, Froc. Nat 'I Acad. 



