112 Experimental Zoology 



Type 3 might give types 345 



Type 4 might give types 4 



Type 5 might give types 4 5 



Type 6 might give types 4567 



Type 7 might give types .4 67 



Thus the wild type i is dominant to all the others, i.e. its 

 offspring may belong to any one of the other types which must 

 have been recessive in its germ-cells. The gray forms i, 2, 3, 

 are also dominant, in the same sense, to the black forms. The 

 albinos give albinos only. " It appears that types 3 and 5 could 

 be ultimately bred true. As to 6 and 7, the evidence is not very 

 clear ; but as I understand the account, neither was completely 

 freed from throwing the other. The breeding in these types 

 was the least successful and extensive. Possibly they are illus- 

 trations of the Mittel-rassen of de Vries. It is especially 

 noteworthy that the gray-and-white type 3 and the black-and- 

 white type 5 do not give rise to self-gray gametes or to self- 

 black gametes, a fact found again in mice. We see, therefore, 

 that there are gametes for black-and-white and for gray-and- 

 white, each of which may behave as a single character and domi- 

 nate over albino." * 



When pure black-and-white rats were crossed with the wild 

 gray rats, all the colored types might appear in generation (F 2 ) 

 except albinos. In other words, the black-and-white do not 

 separate, they are not resolved in the germ-cells, as other experi- 

 ments also indicate. Crampe found further that black-and- 

 white individuals that gave albinos in the first generation when 

 bred inter se also gave albinos when bred to albinos. In this 

 case the black-and-white individuals had probably arisen from a 

 cross between black-and-white and albino, so that the albino 

 (and not the white of the black-and-white) gave the white mice 

 just mentioned. On the other hand, Crampe found that when 

 the black-and-white rats did not themselves throw albinos, they 

 did not do so in the first generation when bred to albinos. 



1 Bateson, Proc. Zool. Soc. 



