C. C. I.ITTLK 287 



the pniduction of ii t4)rt4)iHi»-Hhell iiml(\ iinthing that omld hti|)|icn in 

 either the gnnu*U>8 of i\\v bhick timlr or of t hi* t/ort/oiw-Hhrll rrnmlc wotiM 

 pnxluoo )i Uirtoiw-shrll iiwilr. On Whiliii^'s hy|H»lh«*HiM wr Mhniild hiivr 

 to8UppoH(> that thi* tottoiso-Hhrll tciiiair, altJimi^h slw htrHilf .shnwiMl no 

 innrkiHi luotiiHorH (t»r »\\v would have bmi hiack), tranMinilM uiiUMually 

 hwivy iiHHiiliors to hiT «ous. Thosr ^jinu-U's wcuiM in turn havr to Im- 

 mot by an iMjually hoavysi'toi* uKMlificr.s from tin- black inaN*, or a yrllow 

 would result. 



Further than this, by Whiting's hy|)oth('His thf yellow male is YXt) in 

 constitution, and this makes th«' soiin-e of the black that he must pnMliiee 

 fKunatieally under the mfluenee of mcMlifiji-s in onler to ln'come a tortoise- 

 shell, uncertain. This condition is, of coui-se, not im|)o8sible but is highly 

 impmlmble. Finally, the phenomenon of non-disjiuiction meets with 

 distinct dirticulties. Unless the black male forms gametes with neither 

 the A' nor 6 chromosomes present it would be hard to sec how the 

 tort-oise-shell male could be prmluced by this mating. Fijrmation of 

 sperm without A' or 6 would not be likely. Yet the {wssibility exists 

 and may therefore be considered. What seems to me altogether more 

 likely is that the breeder's records on which Doncjister bjised his obser- 

 vation were in this aise uncertain or incorrect, a circumstance quite 

 possible in cats even with the best possible intentions. 



(6) The production of fertile tortoise-shell viales. 



We have seen that peculiar tortoise-shell females of formula 



YBXyBXB may possibly be produced by primary non-disjunction. If 



now one of these females is crossed with a black or a yellow male peculiar 



yellow males of the constitution ¥3X66 would be formed iis follows: 



Non -disjunctional 

 Tortoise-shell female crossed with Yellow male 



YliXyliXd YBXe 



Forming gametes YBXyliX, YliXO, Forming gametes YliX and 

 YliX, 0, yliXd and yliX 



Zygotes (a) YliXyBXYBX Dies 



(6) YBXdYBX Peculiar yellow female 



(c) YBXYBX Yellow female 



(d) 6 YBX Yellow male 



(«) YBXyBXd Peculiar tortoise-shell female 



(/) YBX ee Peculiar yellow male 



(g) YBX d Yellow male 



(h) ee Dies 



(i) yliXeYBX Peculiar tortoise-shell female 



(j) yBXee Peculiar black male 



(Jk) yBXYBX Tortoise-shell fumale 



{I) yBX e Black male 



