Sex-limited inheritance in Lychnis dioica L. 291 



which X represents the gene for sex (Morgan 1912 b, Mokg^vk and 

 Lynch 1912, Little 1912), or when for orange pigmentation appears 

 together with X in the genetic formulae used by a writer who has fre- 

 quently used to represent the absence of X (Morgan 1911c). 



Aside from formulae whose manipulations involve assumptions of 

 selective fertilization (Castle 1903, Doncaster and Raynor 1906, 

 GooDALE 1910, Doncaster 1911, Schleif 1912), reversible dominance 

 and changing potencies of determiners (Smith 1910, de Meijere 1911, 

 Goldschmidt 1912, Strong 1912 a, b), — processes having no adequate 

 experimental support and too elusive to be of use in working out genetic 

 problems, six tlifferent types of formulae may be used to represent the 

 genotypic relations between the sexes, — three for those cases in which 

 the female is a sex -homozygote and three for those in which she is a 

 sex -heterozygote. Several of these formulae have appeared in many 

 variations, while others have been little used and consequently have 

 few synonyms. The classification of the various formulations given 

 below is intended to be fairly comprehensive, but not exhaustive. Since 

 chromosome -terminology has been blended with the genetic, both are 

 included. For this reason it has not always been easy to decide where 

 a particular formula should be placed, since some of those who have 

 discussed the cytological phenomena have carefully avoided committing 

 themselves regarding the functions of the Y-chromosome. For the sake 

 of the classification I have assumed that the Y-chromosome is sexually 

 indifferent, as that seems to be the view generally held by those who 

 have discussed the cytological basis of sex-determination. The division 

 into those cases (A) in which the female is homozygous, and (B) in 

 which she is heterozygous, now rests upon such a large body of har- 

 monious e\idence, that it must be accepted as a natural division; but 

 the three sets of formulae available for each of these natural divisions, 

 are largely hypothetical and may be used interchangeably for nearly all 

 of the cases thus far investigated. These three hypothetical formulations 

 differ from each other according as they assume that a member of the 

 homozygous sex is a positive, a negative, or a neutral, liomozygote. 



A. The female is homozygous, the male heterozygous. 



Examples: Bryonia, Lychnis, Nematoda, Crustacea, Myriapoda, Arachnida, 



Odonata, Orthoptera, Hemiptera, Diptera, Mammalia. 



1. The female is assumed to he a positive homozygote. 



Model formulae: XXFF == 9, XXFf = cT, 



or simply, FF = 9 , Ff = (f. 



