58 A. H. STURTEVANT 



SIBIMARY 



It has been found possible to arrange six sex-liked factors in 

 Drosophila in a linear series, using the number of cross-overs 

 per 100 cases as an index of the distance between any two factors. 

 This scheme gives consistent results, in the main. 



A source of error in predicting the strength of association be- 

 tween untried factors is found in double crossing over. The 

 occurrence of this phenomenon is demonstrated, and it is shown 

 not to occur as often as would be expected from a purely mathe- 

 matical point of view, but the conditions governing its frequency 

 are as yet not worked out. 



These results are explained on the basis of Morgan's 

 application of Janssens' chiasmatype hypothesis to associative 

 inheritance. They form a new argument in favor of the 

 chromosome view of inheritance, since they strongly indicate that 

 the factors investigated are arranged in a linear series, at least 

 mathematically. 



November, 1912. 



LITERATURE CITED 



BovERi, T. 1902 UebermehrpoligeMitosenalsMittel zur Analyse desZellkerns. 

 Verh, Phys.-Med. Ges. Wiirzburg., N.F., Bd. 35, p. 67. 



Dexter, J. S. 1912 On coupling of certain sex-linked charaters in Drosophila. 

 Biol. Bull., vol. 2.3, p. 183. ** 



Janssens, F. A. 1909 La theorie de la chiasmatypie. La Cellule, torn. 25, p. 

 389. 



LocTC, R. H. 1906 Recent progress in the study of variation, heredity, and evo- 

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McClung, C. E. 1902 The accessory chromosome — sex determinant? Biol. 

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Morgan, T. H. 1910 Sex-limited inheritance in Drosophila. Science, n.s., vol. 

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1910 a The method of inheritance of two sex-limited characters in 

 the same animal. Proc. Soc. Exp. Biol. Med., vol. 8, p. 17. 



1911 The application of the conception of pure lines to sex-limited 

 inheritance and to sexual dimorphism. Amer. Nat., vol. 45, p. 65. 



