INHERITANCE OF DILUTION. 83 



(CC r Dd) or dilution and albinism (CC a Dd), or if a dilute can be obtained 

 which transmits both red-eye and albinism (C r C a Dd), the hypothesis 

 of modifiers must be adopted. But all attempts to obtain these double 

 heterozygotes have failed . All of the results substantiate the hypothesis 

 of quadruple allelomorphs. 



Arequipa male No. 1007 was of formula C r C r DD or C d Cd, depending 

 on the hypothesis chosen (see crosses 28 to 34) . He was crossed with 

 intense guinea-pigs of BW or 4-toe stock, known to transmit no dilu- 

 tion (CC a dd or CC a ) . The intense young could only be CC r Dd or CCd 

 under the two hypotheses. Five of them were crossed with albinos and 

 gave 13 intense, 20 dilute young, no others (cross 34). Expectation 

 on the hypothesis of a modifier is 16 intense, 8 dilute, 8 red-eye. On 

 the hypothesis of allelomorphs it is 16 intense to 16 dilute. Both the 

 excess of dilutes and the absence of red-eyes point conclusively to the 

 latter. 



In cross 18, intense guinea-pigs, each of which had a dilute parent 

 known to transmit albinism and with no lea or Arequipa blood, are 

 crossed with albinos or red-eyes. Under the modifier hypothesis we 

 would expect about half of them to be CC a Dd. Under the allelomorph 

 hypothesis, they should be CC d or CC a . As it turned out, there were 6 

 which gave only intense and dilute (30 intense, 35 dilute) and 8 which 

 gave no dilute young (57 intense to 61 red-eye or albino). Thus there 

 was no intense which had dilute young and also red-eyes or albinos. 

 This result distinctly favors the hypothesis of allelomorphs. 



In crosses 19 and 27 dilutes, each from the cross of a red-eye with a 

 stock guinea-pig free from South American ancestry, are crossed with 

 albinos. Under the modifier hypothesis, those which transmit red-eye 

 at all are necessarily C r C a Dd, for they must be C ra C ra D in order to 

 appear dilute; they could get C a , but not C r , from the stock guinea-pig 

 parent, and they would necessarily get d from the red-eye parent. 

 Under the allelomorph hypothesis, they should be CdC r , the rest CdC a ; 

 9 gave only dilutes and red-eyes (18 dilutes, 24 red-eyes); 9 others 

 gave only dilutes and albinos (20 dilutes, 16 albinos). There were 3 

 which had had only 8 dilute young when tabulated. The fact that 

 none of the 9 which had red-eye young also had albinos among 42 

 young gives a third body of evidence pointing toward the allelomorph 

 hypothesis. 



These results make it reasonably certain that the allelomorph hypo- 

 thesis is correct. The only other possibility would involve coupling so 

 close as to simulate multiple allelomorphs. The hypothesis of allelo- 

 morphs has been reached by a method of elimination. It remains to 

 show that all of the data are in harmony with it. In the next section, 

 definite conclusions are reached as to the inheritance of variations in 

 intensity and dilution which make it possible to distinguish intense 

 animals from dilute in all but very exceptional cases. 



