June 30. 192 1] 



NATURE 



571 



Bureau for research, as research is ordinarily under- 

 stood, but owing to the nature and extent of the 

 machinery which it has at its disposal, including its 

 corresponding members throughout the Dominions 

 and Colonies, its technical advisory committees — 

 active bodies comprising some 151 members, who are 

 among the leading authorities on the respective 

 minerals and the industries connected therewith — it is 



in an exceptional position for disseminating sugges- 

 tions, shaping problems to which they give rise, and 

 carrying out the necessary preliminary surveys, with- 

 out which it would be difficult to advise as to whether 

 a problem should be brought before organisations 

 such, for instance, as the Department of Scientific 

 and Industrial Research, the province of which is the 

 carrying out of research. 



The Genetics of Sex. 



By Prof. R. Ruggi.es Gates. 



''F'HE investigation of the chromosomes in a large 

 ■*■ number of insects and other animals has shown 

 that the so-called X- and Y-chromosomes furnish a 

 mechanical basis for the determination of sex in the 

 fertilised egg, its inheritance in later generations, and 

 the usual occurrence of approximate equality of the 

 two sexes when one of them is heterozygous (XY or 

 XO). The fundamental character of this relation 

 between the X- and Y-chromosomes and sex is now 

 generally admitted. It would appear that the differ- 

 ence in the chromosome content of the nuclei in 

 the two sexes affects the metabolism during develop- 

 ment in such a way as to produce one sex or the 

 other, and in some groups to affect the secondary 

 sexual characters as well. Combined cytological and 

 breeding investigations have shown further that in 

 most insects and mammals, including man, the male 

 is the heterozygous sex, while in the Lepidoptera and 

 birds the female is heterozygous. 



Recent work on the subject of sex in animals 

 accepts this situation, and is building upon it a further 

 analysis of sex-differences. The most active lines of 

 work have been (i) in connection with the discovery 

 and interpretation of intersexes in various animals 

 and plants, and (2) in the explanation of the depar- 

 tures from equality in the numbers of the sexes under 

 a variety of conditions, normal or experimental. It is 

 now clear that these results do not negative a 

 chromosome hypothesis of the fundamental distinc- 

 tion between the sexes, at least in animals, but rather 

 supplement it in an important way. Sex intergrades 

 have been studied bv Goldschmidt in the Gipsy moth, 

 by Banta in Daphnia, and by Sturtevant and others 

 in Drosophila ; also in plants there have been the 

 studies of intersexes in Mercurialis by Yampolsky 

 and in Plantago by Bartlett and others. These in- 

 vestigations are still in progress, and it is only neces- 

 sary to say that they are not out of harmony with 

 a chromosome hypothesis of the origin of the sex- 

 differences, although the situation in plants remains 

 to be cleared up. 



Of more immediate interest here are the cases 

 where one of the sexes preponderates. Mr. Julian 

 Huxley (see reference in Nature, March 24, p. 116) 

 has recently shown how in the millions fish (Girardinus 

 poeciloides) a great preponderance of females, fol- 

 lowed by a lesser preponderance of males, and finally 

 by equality of the sex-ratio, can be best explained by 

 assuming that the chromosome-constitution of the in- 

 dividual has been temporarily overridden by external 

 influences. The important work of Riddle in con- 

 trolling the sexes in pigeons may ultimately receive a 

 similar explanation. 



In an article by Mr. Alan S. Parkes (Science Pro- 

 gress, April, 192 1) the author has applied somewhat 

 similar conceptions to the explanation of the well- 

 known departures from equality of the sex-ratios in 

 man. The statistics from the reports of the Registrar- 

 General, 1838-1914, show an average for this period 



NO. 2696, VOL. 107] 



of 1040 males to 1000 females. There is a similar 

 preponderance of male births in most parts of the 

 world, but in a few regions females preponderate. 

 It is also a remarkable fact that fluctuation in the 

 proportion of male births follows closely the rise andl 

 fall in the price of food. Statistics appear to show 

 further a remarkable rise in the proportion of male 

 births throughout Europe during the war, and it is 

 suggested that war conditions were "in some obscure 

 way beneficial to the welfare of the Y-gametes." 

 That racial differences in the sex-ratio exist is shown 

 by comparing Jews with Christians ; it appears that 

 the former in all countries show a greater excess of 

 male births, while the crossing of races is also 

 known to disturb the sex-ratios. 



From a study of a number of genealogies of British 

 families Mr. Parkes finds that families occur in which 

 the preponderance of males is much greater thaa 

 1040 : 1000, and that this condition is inherite<i 

 through the male, some strongly male-bearing strains; 

 producing more than 58 per cent, in excess of the: 

 above frequency considered as the normal. 



A new type of inheritance of secondary sexuaF 

 characters has recently been discovered by Schmidt 

 (C. r. Trav. Lab. Carlsherg, vol. xiv.. No. 8) in the; 

 fish Lebistes reticidatus from Trinidad. He shows; 

 that the inheritance of a black patch on the dorsali 

 fin of the males in one race is transmitted exclusively 

 from male parent to male offspring, never appearing 

 in the female line at all. This is explained by assum- 

 ing that the spot is determined by the Y-chromosome, 

 for it is distributed in inheritance as the Y-chromo- 

 some is distributed. Hitherto in all cases investigated 

 the Y-chromosome has appeared to be inactive in 

 inheritance, the only evidence against this being the 

 fact that males of Drosophila which lack it ar« sterile. 

 The chromosomes of Lebistes reticidatus are now 

 being investigated. 



On the basis of this result of Schmidt, Castle 

 (Science, April 8, p. 339) has built up an interesting 

 speculation concerning the origin and relationships of 

 the various types of sex-determining chromosomes. 

 Briefly, his suggestion is that the X-chromosome was 

 originally a cytoplasmic body handed on exclusively 

 through the egg, like a plastid, and determining the 

 female condition by its presence. This becomes in^ 

 eluded in the egg nucleus and is duplicated by split* 

 ting, thus giving rise to the condition XX in females 

 and XO in males. If it does not split, a Y element 

 may "develop" as its synaptic mate in the egg» 

 passing later into male offspring, and, through non- 

 disjunction (as in Drosophila), ultimately producing 

 YY males which are assumed to be viable ; they 

 would give rise, as in Abraxas, to the condition in 

 which the female is the heterozygous sex. In criticisnt 

 it may be said that there is no cytological evidence 

 of the transformation of a cytoplasmic body into a 

 chromosome, unless the " chromatoid body " of 

 Wilson be such a case. But it occurs in addition to the 



