80 INHERITANCE IN GUINEA-PIGS. 



has produced yellow. Apparently intense by intense may give any 

 intensity whatever, and almost the same can be said of dilute by dilute. 

 Amid this confusion, however, one cross has been found which con- 

 sistently gives a very definite, although unexpected, result. It is 

 found that a dilute crossed with an albino, even of intense stock, never 

 gives intense young, but only well-defined dilutes and albinos. There 

 are only a few possible ways in which this result can be explained and, 

 from the results of other crosses, all but one of these explanations have 

 been definitely eliminated, namely, that dilution is an allelomorph of 

 albinism. An allelomorph of albinism was already known to be respon- 

 sible for the red-eyed condition in certain South American stocks 

 (Castle, 1914a) . It could now be shown that albinism, red-eye, dilution, 

 and intensity are due to a series of four allelomorphs with dominance 

 in the order of increasing pigmentation. A preliminary account of this 

 demonstration has been given in a previous paper (Wright, 1915). In 

 the present paper the demonstration is given in more detail and further 

 steps are taken in the analysis of the variations. 



THE DILUTION FACTOR. 



The dilute varieties have some resemblance to the red-eyed varieties. 

 The fact that red-eye is due to an allelomorph of albinism suggested 

 that dilution might also be due to a member of the same series of alle- 

 lomorphs. A stock was chosen which was known to carry no dilution. 

 This was the BW stock, which for years has consisted exclusively of the 

 most intense blacks and sooty albinos. The following crosses were 

 designed to eliminate the hypothesis of allelomorphism if incorrect : 



(1) Albinos from intense stock were crossed with dilutes: 



CaCall X CCii = CCali. 



(2) Albinos from dilute stock were crossed with blacks of intense stock: 



CaCaii X CCII = CCali. 



If intensity and dilution form a pair of allelomorphs (I, i) which 

 segregate independently of the pair color and albinism (C, C a ), 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 ; 

 intensity by one parent, dilution by the other. In fact, identical results 

 should be obtained regardless of whether dilution is due to a unit factor 

 or to multiple factors, or even whether its inheritance is Mendelian or 

 not, provided only that it is inherited independently of albinism. 

 Crosses 16 and 17 and table 35 give the actual results. All cases are 

 included, which involve an intense stock known to carry no dilution. 



Among those called dilute below (among the young) , none was more 

 intense than sepia 2 or yellow 4 . Among the intense, none was more 

 dilute than a dull black comparable in grade but not in color with sepia 2 , 

 or a red in very few if any cases as dilute as yellow 2 . There was there- 

 fore no difficulty in drawing a natural line between intense and dilute 

 in these crosses. 



