xm] Intermediates 237 



observer cannot distinguish the DD types from the DRs 

 with fair certainty by a thorough and minute examination. 

 As examples in which heterozygotes are indistinguishable 

 from pure dominants, may be mentioned tall and dwarf in 

 Peas and Sweet Peas, coloured flowers and white flowers 

 in Sweet Peas and Stocks, hoary and glabrous in Stocks. 

 In all these the one " dose " of a dominant factor is sufficient 

 to produce the full effect. 



2. Intermediates due to subtraction- stages of dominant 

 factors, This is also a large and important class, one, too, 

 which has been perhaps more especially a source of the 

 confusion alluded to in the introduction to this section. 

 Of such intermediates the colour of the Dutch rabbit may 

 be taken as a type. The Dutch rabbit has the posterior 

 half of the body coloured, while the anterior half is white 

 except for patches including the eyes and ears. Such a 

 rabbit may be described as in a sense intermediate between 

 the self-coloured rabbit and the albino. Its particoloured 

 nature is due to the restriction of one (or conceivably more) 

 of its pigment-factors to certain areas. In the self-coloured 

 animal this factor has a more extended distribution. But 

 in speaking of the Dutch pattern as an intermediate, an 

 essential point, the definiteness of the Dutch pattern, is 

 missed. It is intermediate only in a strictly limited sense. 

 It is not a transition-stage between a self-colour and an 

 albino, nor would there be any better chance of breeding 

 albinos from genetically pure Dutch than there would be 

 from genetically pure self-coloured rabbits. The Dutch 

 pattern in fact constitutes a definite type and depends for 

 its appearance on the presence of a certain factor in a 

 fairly definite stage, and it does not appear when self- 

 colours are crossed with albinos unless the particular 

 necessary factor in its appropriate stage is introduced in 

 one of the parents. 



Within the Dutch class there are subordinate types 

 again, the interrelations of which have not yet been worked 

 out. Some of these are very probably gametic types which 

 could be bred pure, while others are probably caused by 

 fluctuations of an irregular kind or by the interactions 

 between the factors. It will need very elaborate research 



