Sex-limited inheritauee in Lyrhnis dioica L. 295 



adoption of the "standard" fonnulae. I have introdneed into all the 

 formulae of the sexes used in the present paper, the symbols XX, to 

 call attention to the fact that, whether symbolized or not, the rest of 

 the genotype with which the special factors for sex are associated, is 

 important. This is the XX of Johannsen which represents all those 

 elements or characteristics of the genotype which are not otherwise 

 specifically mentioned in the given formula. They pertain logically to 

 every genetic formula, and when not expressed they must be, nevertheless, 

 always understood as taken for granted. Several writers have introduced' 

 MM or FF into the formulae for both sexes; but in such cases 

 there can be no experimental basis for the assumption of the specific 

 determiners implied by these symbols. All we can say is that in one 

 case XX is essentially njale and becomes female only when brought 

 into relation with one or more added F determiners; and in the other 

 case that XX is essentially female and becomes male only in reactions 

 with added M factors. Whether the essential maleness or essential 

 femaleness of the unanalyzable part of the genotype, is due to the 

 presence of a single pair of F or of M factors, or of forty such pairs, 

 or of none at all, there is in these cases no basis for a judgment. 



As already stated, there are three sets of formulae which may be 

 used in describing the facts of sex -inheritance in any organism, and 

 the choice of a particular formulation must be made arbitrarily, though 

 a decision in favor of one particular set of formulae may be suggested 

 by some feature of the evidence. Thus in those animals in which there 

 is no Y- chromosome in the male, it is natural, though not necessary, 

 to prefer the formulae FF = 9 , and Ff =0". As pointed out by 

 several writers, it is possible to think of the chromosomes as sexually 

 indifferent, — simply as passive indicators of sex, rather than sex- 

 determiners, — and if this be their status no limitation is placed even 

 in these cases, upon the use of the other two sets of formulae. When 

 a Y- chromosome is present, there is no longer such strong reasons for 

 considering the female a positive homozygote, for if the sex-determiner 

 should be related to only a small part of a chromosome, as MORG^VN 

 (1911c) has made plausible, the difference in size of the X- and Y-chromo- 

 somes is no barrier to the inclusion of a male sex-determiner in the 

 Y- chromosome, which is absent from the X- chromosomes, the difference 

 in the size of the X- and Y-chromosomes then pei'haps having I'elation 

 to other factors concerned with the greater anabolic iu;tivity required 

 of the female, or with other secondary sexual relations. This would 

 make the female a negative sex -homozygote, despite the pair of large 



