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CHAPTER 14 



is yes, in the sense that if we could control the 

 genotypes of zygotes we would determine 

 ahead of time what sex would be formed. 

 And again, since X- and Y-bearing sperm of 

 men apparently differ in cytological appear- 

 ance (Figure 14-6; see also Figure 14-7), it 

 should be theoretically possible to separate 

 these, thereby leading to the control of the sex 

 of progeny. Using various animal forms, ex- 

 periments along these lines have been per- 

 formed with some success by Russian, U.S., 

 and Swedish workers using electric currents 

 or centrifugation. Though these methods 

 have given encouraging results, the results 

 are not yet consistent and the techniques not 

 yet suitable for practical use. 



FIGURE 14-7. According to L. B. 

 Shettles, these phase-contrast photo- 

 graphs show a concentric arrangement 

 of the chromosomes present in rounded 

 and elongated types of sperm head. 

 A, B, C, and D from different men. 

 The light, lobulated chains are stained 

 by the Feulgen-Rossenbeck procedure. 



SUMMARY AND CONCLUSIONS 



Genes responsible for sex determination are located not only in the sex chromosomes, but 

 in the autosomes as well. Although sex type may be changed through the action of a single 

 pair of genes, a given sex is usually the result of the interaction of several, and probably 

 many, pairs of genes. Sex is, therefore, a polygenic trait (Chapter 8), in which the usual 

 chromosomal differences found among zygotes serve as visible manifestations of differences 

 in the balance of genes concerned with sex, and by which one balance produces male and 

 another female. Whenever, as in female Drosophila, genie balance is unaffected by the 

 addition or subtraction of whole sets of chromosomes, sex also is unaffected. However, 

 changes in chromosome content which make for intermediate genie balances produce inter- 

 mediate sex types — intersexes; those which make the balance more extreme than normal 

 produce extreme sex types — supersexes. 



