352 EXPERIMENTAL STUDY OF INHERITANCE 



Dominance may not be quite Perfect. — In typical cases the 

 hybrid is exactly like the dominant parent, as when the progeny 

 of grey and albino mice are all grey. In other cases, however, 

 the hybrid, while on the whole dominant, may show some influence 

 of the recessive character, but not nearly enough to warrant 

 us in speaking of a blend. Thus, when white (dominant) 

 Leghorn poultry are crossed with brown (recessive) Leghorn, 

 most of the offspring have some " ticks " of colour. When these 

 are inbred they produce a quarter brown (extracted recessives) 

 and three-quarters pure white or white with a few ticks. The 

 dominance is not quite perfect, but this, Mr. Punnett says, 

 " makes no difference to the essential feature of Mendel's 

 discovery, which of course is the segregation of the dominant 

 and recessive characters in the gametes " (1905, p. 27). 



Blue Andalusian Fowls. — When black and white fowls are 

 crossed there sometimes results a blue or Andahisian fowl " with 

 a minute patchwork of black and white." When these are inbred 

 they produce 25% black, 50% blue, and 25% white with black 

 splashes. This splitting-up is characteristically Mendelian, but 

 what gives rise to the " blue " feature '.:■ obscure. 



The ingenious Mendelian interpretation in the case of the An- 

 dalusian fowl is that the black and the splashed white are the 

 pure breeds, and that the blue Andalusian is a peculiar mongrel. 

 We must refer to Mr. Punnett's essay on Mendelism for the 

 interesting theoretical working out of the case, which is exceed- 

 ingly instructive, since it shows that Mendelian interpretation 

 is feasible even when the hybrid (the Andalusian) is quite 

 distinct from either parent (black or splashed white). 



Compound Allelomorphs. — A differentiating unit character 

 capable of replacing another or of being replaced by another 

 is technically called a simple allelomorph. But there are other 

 differentiating characters which seem to consist of several 

 components capable of being isolated and of entering into new 

 combinations. These are called compound allelomorphs. 



