310 F. B. SUMNER AND H. H. COLLINS 



tested and, 2) the behavior of the color differences entering into 

 subspecific crosses has been determined with more precision. 

 Investigations are under way which may settle some of these 

 questions. 



ALBINO-YELLOW CROSSES 



Matings of three yellows and four albinos resulted in the birth 

 of thirty Fj offspring, of which twelve males and eleven females 

 have lived to maturity. All are of the wild color, and would 

 pass for normal gambeli. 



Thus far, the Fg generation consists of 83 individuals, of which 

 52 are normal (wild color), 13 yellow, and 18 albino. On the 

 assumption that these factors are not linked, the 'expected' 

 numbers are 47, 16, and 21, respectively. The departure from 

 expectation is doubtless accidental. In any case, there is no 

 evidence of linkage, the occurrence of which would have reduced 

 the proportionate number of dark individuals, instead of increas- 

 ing it. 



The number of F2 albinos and yellows which have thus far 

 been tested for linkage is very small, but it is of interest that 

 the proportion of recombinations is even greater than would be 

 expected from random assortment (Sumner, '22). Thus the 

 meager data at hand make it plain that no considerable degree 

 of linkage, if any, exists between these factors. 



ALBINO-PALLID CROSSES 



Matings of five pallids and two albinos resulted in the birth 

 of nineteen young (11 c?', 8 9 ), all fully pigmented mice, having 

 the appearance of ordinary normal gambeli. 



It is of interest that conclusive evidence was found for a high 

 degree of linkage between the palUd and the albino factors 

 (Sumner, '22). 



Only sixteen F2 young have thus far been reared, derived from 

 simple Fi X Fi matings, though a considerable number of a 

 somewhat more complex pedigree were obtained. Of these six- 

 teen, 9 were dark, 6 pallid and 1 albino. The abnormal propor- 

 tions of the two recessive classes is doubtless a chance result due 



