200 Outline of Genetics 



''It is not the simple possession of two X chromosomes 

 that makes a female, or of one that makes a male. The 

 preponderance of genes that are in the autosomes tends 

 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 autosomes 

 produces a female, while iX : 2 sets autosomes produces a 

 male. An intermediate ration, 2X13 sets autosomes, 

 produces an intermediate condition, the intersex." 



''The fourth chromosome seems to have a disproportionately 

 large share of the total male-producing genes; for there are indica- 

 tions that the triplo-fourth intersexes are preponderantly of the 

 'male' type, while the diplo-fourth intersexes are mainly 'female' 

 type." 



According to this conception, 3 A': 2 sets autosomes should be 

 " superfemales " and iX:3 sets autosomes should be "supermales." 

 Bridges has actually identified such types, both being sterile. 



It is certain that this conception will exert a far-reaching influ- 

 ence upon the existing ideas of sex detemination. In the first 

 place, it gives a somewhat more exact idea as to the elements 

 effective in determining sex. Hitherto it had been thought, 

 rather vaguely, that the X chromosome determines sex either per 

 se or by virtue of some special factor which it contains. It is 

 interesting now to realize that a number of factors may be influ- 

 encing sex in one direction or the other, and perhaps that these are 

 identical with factors which have previously been known as playing 

 another role. A different rate of metabolism has commonly been 

 associated with the two sexes; a study of the influence of specific 

 factors on metabolic rate now becomes significant in this connection. 



In the second place, it furnishes an exact interpretation of 

 intersexes on a chromosome basis. Hitherto intersexes have 

 usually been interpreted in rather vague physiological terms, and 

 have been used as an argument against the sex chromosome theory 

 (or have been harmonized with the sex chromosome theory only 

 by the assumption of some additional extra-chromosomal influ- 

 ence — GoLDSCHMiDT 13). Bridges' Conception now paints a 



