194 



MENDELISM 



characters at once. A pair of individuals may, how- 

 ever, between them carry all the possible colour 

 allelomorphs. Cuenot gives the following example, 

 being one of three possible methods by which all the 

 three colours, yellow, grey, and black, as well as the 

 albino character, can appear among the offspring of a 

 single pair of animals : 



Parents : A G (albino) AN (albino) 

 F! AC. AN 



Gametes 



AG 



AN 



CN (black) AJ (albino) 

 CN .AJ 



CN AJ CJ AN 



The actual numbers of offspring which were obtained 

 in F 2 fromt his cross were as follows : 81 albinos, 

 34 yellow, 20 black, 16 grey ; the expected proportion 

 being 76 : 38 : 19 : 19. 



By the process of crossing followed by selection of 

 those families in which a uniform series of young 

 appeared in F 3 , Cuenot was able to extract without 

 difficulty pure homozygous races of blacks CN . CN, 

 and of greys CG . CG, as well as the corresponding 

 albino races AN . AN, and AG . AG. But in the case 

 of the yellow a curious and unexpected phenomenon 

 appeared, and one which, if Cuenot's explanation of it 



