CASTLE AND ALLEN. — THE HEREDITY OP ALBINISM. 619 



It is not necessary to suppose, as Mendel apparently did, that the 

 segregated elements of a composite character pass invariably into different 

 gametes. There is reason to believe that yellow is frequently, if not 

 always, latent in black mice, and black in yellow mice, though such an 

 occurrence has not yet been conclusively demonstrated. 



We would not, however, deny the possible correctness of Mendel's 

 explanation in other cases. This should be indicated in breeding experi- 

 ments by the simultaneous appearance in different individuals of the 

 segregated elements of the composite character, and in particular numer- 

 ical proportions. Each new sort should be incapable of producing the 

 other, under either close or cross breeding. This is a subject well merit- 

 ing more careful investigation. 



VII. Summary. 



1. Complete albinism, without a recorded exception, behaves as a 

 recessive character in heredity. 



2. Partial albinism is a mosaic condition in which the dominant pig- 

 ment-forming character and the recessive albino character are visible in 

 different parts of the same individual. 



3. Pure mosaic individuals form only gametes which partake of their 

 own mosaic nature. They and their gametes may be designated D R. 



4. Hybrid mosaics result from the union of a mosaic gamete, D R, 

 with a recessive gamete, R, as in a cross between a 23ure mosaic and a 

 recessive individual. Such crosses are made when a race of spotted 

 mice which breeds true is crossed with albinos. 



5. Hybrid mosaic mice are usually more extensively pigmented than 

 pure mosaics, frequently they are pigmented all over. When they are 

 spotted with white, we may consider this the result of dominance of the 

 mosaic gamete as a unit and may designate them accordingly, D R-{R). 

 When they are pigmented all over, it is clear that the dominant element 

 only of the mosaic gamete is visible in them. They should then be 

 designated D{R)\R). 



6. The gametes formed by a hybrid mosaic are of two sorts, like those 

 which united to produce it, namely, D R and R. Accordingly when 

 hybrid mosaic individuals breed together, they produce offspring of three 

 different sorts, — pure mosaics, hybrid mosaics, and recessives. We should 

 expect these three classes to be numerically as 1 : 2 : 1, and this is probably 

 the case. When a hybrid mosaic is bred to a recessive, two sorts of 

 offspring are produced, — hybrid mosaics and recessives. These classes 

 should be of approximately equal size. 



