No. 530] 



CONCEPTION OF PURE LINES 



77 



posite sides (or enter the chromosome sometimes one 

 way and sometimes the other). All the genes contained 

 in the X-chromosomes can thus shift in the female be- 

 cause in this group two X's are present. Sex-limited 

 inheritance is only possible where similar conditions 

 exist (either in the male or in the female) and since in 

 man color blindness follows the same scheme as does 

 white eyes in my flies, we have an experimental proof that 

 in the male of homo sapiens there is only one X-chromo- 

 some, and this, in fact, Guyer has just shown to be the 

 case from cytological evidence. But by parity of rea- 

 soning it is the female in Gallus bankiva that should have 

 only one X present, but Guyer is persuaded that here too 

 (at least in the race of fowls he studied) the male has 

 only one X-chromosome. There is then in this case a 

 contradiction between the experimental evidence and that 

 furnished by cytology and it remains to see which is 

 correct. 



Bateson has shown that some of these cases of sex- 

 limited inheritance can be explained on the grounds that 

 there is a repulsion between the female-determining fac- 

 tor and that character that is sex-limited. The view that 

 I maintain does not involve the idea of a repulsion be- 

 tween unlike elements, not allelomorphic. Spillman's 

 hypothesis also involves this idea of repulsion between 

 unlike elements. On my view, on the contrary, an at- 

 tempt is made to show how the results may be due to a 

 connection existing between certain material bodies in 

 the egg ; a connection that is consistently carried through 

 successive generations, and subject only to the ordinary 

 interchange of genes between homologous chromosomes 

 (when a pair of chromosomes is present). 5 



For several years it has seemed to me that the chromo- 

 some hypothesis, so called, could not be utilized to ex- 

 plain the Mendelian results in the form presented by 



• The hypothesis advanced here to explain sex-limited inheritance applies 

 also to Abraxas if the latter follows the Fmfra scheme and if in the egg 



