Sex-limited inheritance in Lychnis ilioica L. 273 



leafed plants which bloomed consisted of 12 9 and 8 r?, thus showing 

 that in his cultures, as in mine, the Fo progeny consisted of three 

 phenotypes, broad-leafed females, broad-leafed males and narrow-leafed 

 males, and in my cultures, in which there had been no selection, the 

 ratios of these types, 32 : 11 : 6, gave as near approach to the expected 

 ratios, 25 : 12 : 12, as the smallness of the numbers requires. 



To one familiar with the characteristic ratios in sex -limited in- 

 heritance, this result in the F2 is at once a sufficient demonstration 

 that the females are sexually homozygous and the males heterozygous, as 

 I had already decided to be the case from my investigations of the genetic 

 relations of the hermaphrodites (Shull 1910, I'Jll). The situation may 

 be illustrated schematically by the conventional method, assuming that 

 the female is a positive homozygote, XXFF^), and the male a hetero- 

 zygote, XXFf, and that the determiner of the typical broad leaves, B, is 

 coupled-) with the sex-gene, F. We have then the somatic formula of the 

 normal female XBF .XBF and that of the normal male either XBF .XBf 

 or XBF . Xhf. The mutation by which the narrow-leafed form was pro- 

 duced, consisted in the disappearance of the gene B from its association 

 with the sex-gene F, (and from f, the homolog of F, in case the normal 

 male has the first of the two mentioned formulae, XBF .XBf). As it 

 is easier to comprehend a mutation wliich results in the loss of a single 

 gene than the simultaneous loss of two genes, we will, for the sake of 

 the present schematic representation, adopt the second formula for the 

 normal male, XBF . Xhf. Then the narrow-leafed male which had lost 

 the B from its BF gene, will have the formula XhF . Xbf and will pro- 

 duce sperms of two kinds, XbF and Xbf, while the broad-leafed female 

 produces only one sort of egg, XBF. The Fi produced by the union 

 of broad-leafed females and narrow-leafed males will consist, therefore, 

 of heterozygous broad-leafed females, XBF. XhF, and heterozygous broad- 

 leafed males, XBF. Xbf. 



') The "XX" in my formulae represent the unanalyzed rest of the genotype. 

 They can be omitted without in any way affecting the manipulation of the formulae, 

 but it must not be forgotten that they are a part of every Mendelian formula, whether 

 expressed or omitted in the written symbols. 



^) It must be understood that this is a figurative expression, as all the known 

 facts will be' met quite as well by assuming that the gene F itself determines not only 

 the sex, but also the broad leaves. On the latter assumption, the narrow-leafed condition 

 must result from a modification of the gene F, as a result of which it no longer produces 

 such great breadth of leaves as before, though continuing to have the same relation to 

 the determination of sex. 



