ROUGH FUR. 



113 



smooth parent of such a stock as 4-toe. The parents and offspring of 

 rough E (SS) must necessarily have at least one S (SS or Ss), while 

 full-roughs and 4-toe smooths are ss. The three exceptional rough E's 

 can only be interpreted as extreme minus fluctuations of type RrSs. 



(10) Occasionally a smooth from a cross which produces rough E will 

 transmit the rough factor, breeding like a rough E. The discovery of a 

 smooth (RrSS) which had a rough C young one (RrSs) when crossed 

 with a 4-toe smooth (rrss), apparently violating the dominance of 

 roughness, is the kind of exception that proves the rule, coming as it 

 did where predicted. 



The descendants of male 4003 illustrate the theory very well. He 

 was of constitution RRSS by theory. 



Table 56. 



Of those called rough B, 2 were close to rough A and 3 were close to 

 rough C. 



POSSIBILITIES OF LINKAGE AMONG ROUGH AND COLOR FACTORS. 



In the mating just cited, factors R and S enter the cross from the 

 same individual. The excess of full-roughs (Rss), probably 10 where 

 7 are expected, makes any linkage between R and S very unlikely. 

 Another test is furnished by the cross of double heterozygotes, RrSs 

 with 4-toe smooths, rrss, where it is definitely known whether R and S 

 enter the cross together or apart. Cases which should show coupling 

 if there is linkage are cross 54-1, 2, 4, 5, 6, 12, 15, 16, 17, and cross 

 72-5, 6, 7. Cases which should show repulsion are cross 61-1, cross 

 64-1, 3, and cross 72-1, 2, 8, 9, 10. 



Table 57. 



The indication of linkage is too slight to be considered significant, 

 especially in view of the excess of cross-overs in the F 2 data. 



Thus there is probably no linkage between R and S. It is interesting 

 to analyze the data with regard to possible linkages of these factors with 



