No. 579] ALBINO SERIES OF ALLELOMORPHS 



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binism because of the stock albino parent, should not be 

 able to transmit red-eye. As for hypotheses of linkage, 

 it need only be said that no results have been obtained 

 which require them. The critical crosses have all been 

 made reciprocally as regards sex. 



The fact that dilutes are more or less intermediate be- 

 tween intense and red-eye varieties suggested the fol- 

 lowing experiments which were designed to demon- 

 strate at once whether there was any relation in inheri- 

 tance between albinism and dilution. Dilutes were crossed 

 with albinos from certain stocks which for years had given 

 only intense and albino young, but no dilutes. Second, 

 intense pigs from these same stocks, which had given only 

 intense and albino young, were crossed with albinos from 

 dilute stock. If intensity and dilution form a pair of 

 allelomorphs which segregate independently of the pair, 

 color and albinism (as is the case in mice and rabbits), 

 these two crosses must give identical results. In each 

 case color is introduced by one parent, albinism by the 

 other; the intensity of certain stocks by one parent, the 

 dilution of certain stocks by the other parent. In fact 

 identical results should be obtained regardless of 

 whether dilution is due to a unit factor or multiple fac- 

 tors, or even whether its inheritance is Mendelian or not, 

 provided only that it is inherited independently of albinism. 

 As it happened, these two crosses gave strikingly differ- 

 ent results. The first cross, viz., dilute by albino from 

 intense stock, gave only dilutes, 37 in number, aside from 

 albinos. The second cross, intense from intense stock 

 by albino from dilute stock, gave only intense young, 49 

 in number, aside from albinos. These different results 

 can only be explained by assuming that a member of the 

 albino series of allelomorphs, recessive to intensity, is 

 essential to dilute animals. Thus genetically, dilution 

 may be albinism plus a modifying factor, or it may be 

 red-eye plus a modifying factor, or it may be a new allelo- 

 morph. The last has proved to be the case. A large 

 number of intense animals, at least half of which under 



