GAMETIC PURITY 157 



albino) females are crossed with cinnamon males, both greens and 

 cinnamons are invariably female. When cinnamon females are 

 crossed with green males the young are always green." 1 The 

 instance " most familiar amongst animals is perhaps that of the 

 Mule (Mare and Jackass) and the Hinny (She-ass and Stallion) 

 and amongst plants the hybrids of Digitalis." 2 



265. Dominance may be influenced by race. " While long tail 

 and crest feathers are dominant in poultry, long hair (equally due 

 to the prolonged life of the follicle) is recessive in mammals (Castle, 

 J903, 1905; pp. 64-7, 73-4; Hurst, 1904). White is usually 

 recessive to pigment in flowers and mammals, but is usually 

 dominant to pigment in poultry." 3 " Yellow (beak and foot colour) 

 of the white Leghorn dominates over black of the Minorca, but 

 yellow of the dark Brahma is dominated by the Minorca." 4 



266. Dominance may be affected by the idiosyncrasies of the 

 parent. " In all cases as yet investigated (in poultry) individuals 

 differ greatly in the results they give, and we can only suppose that 

 these differences represent different proportions in the number of 

 effective dominant and recessive germs which they produce." 5 



267. Lastly, in some cases it is difficult to say which of a pair 

 of characters is dominant, since both are patent in about equal 

 numbers in the first mongrel generation, as in the case of a sixth 

 digit in man or a fifth toe in poultry. Even when a character is 

 usually strongly dominant over its alternative, recessive individuals 

 sometimes appear in the first mongrel generation. 6 



268. To sum up : it is very evident that " Dominance is a 

 matter of degree, not of kind ; " 7 " Dominance is a phenomenon 

 presenting various degrees of intensity." 8 



269. We have next to consider the hypothesis of gametic purity 

 a hypothesis which implies that the pure dominants and recessives 

 which spring from impure dominants of the first and succeeding 

 mongrel generations, extracted pure dominants and recessives as 

 they are called, inherit only one kind of unit out of each pair of 

 alternative units, and therefore (as regards each separate character) 

 are in effect derived from only one of the crossed ancestral lines. 



1 Second Report to Evolution Committee, p. 128. 



2 First Report to Evolution Committee, p. 132. 



3 Davenport, Inheritance in Poultry, p. 132. 



4 Ibid., p. g/. 



5 First Report to Evolution Committee, p. 106. 



6 First Report to Evolution Committee, pp. 1 19 et seq. 



7 Inheritance in Poultry, p. 85. 



8 First Report to Evolution Committee, p. 126. 



