No. 646] LINK A GE IN PEROMYSCUS 



417 



of linkage, the occurrence of which would have reduced 

 the proportionate number of dark individuals, instead 

 of increasing it. 



The number of F2 albinos and yellows which have 

 been thus far tested is very small, but it is of interest 

 that the proportion of recombinations is even greater 

 than would be expected from random assortment. In- 

 clusion of these meager results in the present report 

 seems justified by the probability that we shall not soon 

 rear any considerable number of hybrids between the 

 yellow and albino varieties. 



Seven extracted albinos have been mated with pure 

 yellows. Three of these have given only yellow offspring, 

 the numbers being 9, 13 and 21, respectively. Thus, three 

 of these seven albinos are, in all probability, double re- 

 cessives {ccyy). (One in four should be double reces- 

 sives, according to chance.) Three other albinos have 

 given mixed offspring. They are evidently of the for- 

 mula ccYy. The remaining one appears to have the for- 

 mula ccYY, as judged by the production of 15 dark young. 



Two extracted yellow females mated with a (sup- 

 posedly) pure albino male gave birth to 4 albinos and 4 

 dark.^3 albinos would be expected here if linkage 

 were complete, while only one third should be albinos 

 in the total absence of linkage. Thus the number of re- 

 combinations is again too high, even on the assumption 

 of no linkage. 



These numbers are, of course, very small. But even 

 here such proportions would have been quite improbable 

 had any marked degree of linkage existed— such, for ex- 

 ample, as has been found to exist between the pallid and 

 albino factors. 



13 It is only fair to add that 4 yellows likewise resulted from these ma- 

 tings. This was doubtless due to the fact, unsuspected at the time, that 

 the albino male carried the "yellow" factor, one of his two great-grand- 

 parents having been heterozygous for yellow. 



