396 MENDEL'S LAW AND THE HEREDITY OF ALBINISM. 



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

 in other cases. This should be indicated in breeding experiments by the simultaneous 

 appearance in different individuals of the segregated elements of the composite char- 

 acter, and in particular numerical proportions. Each new sort should be incapable 

 of producing the other, under either close or cross breeding. This is a subject well 

 meriting more careful investigation. 



VIII. 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 pigment-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 DR. 



4. Hybrid mosaics result from the union of a mosaic gamete, DR, with a recessive 

 gamete, R, as in a cross between a pure 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, 

 jrequently 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, DR-(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, DR 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. 



7. Albinism apparently complete may in reality conceal traces of the pigment- 

 forming character either in an active or in a latent condition. Albinos that are thus 

 constituted are in reality mosaics of the contrasted characters, but with the pigment- 

 forming character (ordinarily dominant) occurring in a condition of partial or com- 



