No. 546] SHORTER ARTICLES AND DISCUSSION 369 



If yellow mice of the sort one usually obtains be bred togei her 

 they produce yellows, blacks and chocolates — almost never any 

 agoutis. But if such yellows be bred to agoutis and their yellow 

 offspring be mated together the result is only yellows and 

 agoutis. It has been pointed out by Morgan 4 that this last result 

 is inconsistent on the current formulae, since blacks or chocolates 

 should also be expected. For example, if we assume, as I think 

 we must, that ordinary yellow mice usually have the constitution 

 Yt yt, then the cross under discussion would be as follows: 

 Yellow— r* yt 

 Agouti— yr yT 



Total, omitting all FF's: 8 yellows, 3 agoutis, 1 black or chocolate. 



It seems to me that the easiest way of explaining why this 

 mating actually does not produce Macks ;md chocolates is by the 

 assumption of linkage or association ("gametic coupling") 

 between the agouti and yellow factors. The fanciers, from whom 

 most yellows come, ordinarily keep few agouti mice. It is there- 

 fore probable that most yellows carry no T, and for this reason 

 Y and T really show "spurious allelomorphism" or repulsion 

 instead of "gametic coupling."" There seems to be no evidence 

 that T and T ever occur in the same gamete. The evidence 

 which has led to this conclusion is as follows : 



Miss Durham 6 has found that if ordinary yellows be mated 



