No. 572] 



MULTIPLE ALLELOMORPHS 



455 



"We are justified, therefore, in treating gray white-belly 

 as an allelomorph of gray gray-belly, the former domi- 

 nating. If crossing over should occur, it might perhaps 

 only be realized in the gray or cinnamon mice, since it is 

 possible that the ticked condition of the hair (that is, 

 common to gray and to cinnamon) is necessary to realize 

 this condition. The expected crossover that would be 

 observed would be gray gray-belly mice. The contrary 

 class would then be black or chocolate mice that carry 

 the factor for white-belly that might or might not show 

 the influence of the supposedly separable factor. 



My white-bellied stock of mice had been killed after 

 my earlier results had been published, but Mr. B. B. 

 Horton had kept some of my original stock alive, and 

 from him I obtained a few of these mice in 1912 to carry 

 on the above experiments. 



An extraordinary sex ratio appears in the next to the 

 last table, where there were 26 males to 76 females, ap- 

 proximately 1 : 3. The mice were entered when about 

 three weeks old. The sex was noted, but no special atten- 

 tion given to the determination. There is some chance 

 of mistaking the sex of young mice, but one familiar 

 with these animals can determine with certainty the 

 sex at three weeks if sufficient care is taken. I have no 

 reason to suppose that I made such errors which would 

 have to be frequent to give these results. If taken, then, 

 at their face value, the data seem to show that there is a 

 sex-linked lethal gene present here. It is not linked to 

 any of the factors involved, and this is not expected, 

 since neither black nor agouti is sex-linked. If further 

 work confirms this conclusion (and I hold it as a provi- 

 sional conclusion until it can be further studied) we have 

 here the first evidence of a sex-linked gene in mice. A 

 sex-linked lethal should give a sex ratio of 1<?:2?. 



The Allelomorphism of Yellow, Gray and Black 

 The allelomorphism or "repulsion" of yellow and 

 agouti (gray) may be tested in various ways. One of the 



