46 luherltanve of Coat-Colour in RabbUs 



B. On the "Multiple Allelomorph" hypothesis it must be supposed 

 that we are dealing with three definite factors, any one of 

 which is allelomorphic to any other, so that a given zygote 

 cannot contain more than two of the three. If, following 

 Sturtevant, we denote these factors as S, H, and A, the 

 zygotic constitution, of the three varieties becomes : 



Self-coloured ... SS, 



Himalayan ... ... HH, 



Albino AA. 



The heterozygous self-colour which throws Himalayans is 

 SH, and that throwing albinos is SA : while HA represents 

 the constitution of a Himalayan which throws albinos'. 



It is clear that either hypothesis will cover all the facts. It is 

 equally clear that the " Multiple Allelomorph " hypothesis carries with 

 it the abandonment of the " Presence and Absence " hypothesis, not 

 only in such cases as the present, but in all cases where Mendelian 

 inheritance has been shewn to hold good. For there would appear to 

 be no reconciliation possible between a hypothesis which interprets 

 characters behaving as alternate in heredity, in terms of factors which 

 are alternative in the gamete, and one in which an alternate pair of 

 characters is interpreted in terms of the presence or absence of a single 

 factor. In attempting to decide which of the two views is to be pre- 

 ferred, the rabbit case dealt with in the earlier part of this paper is 

 not without interest. 



In Sturtevant's discussion of the matter he points out that in these 

 cases, where a given character appears to act as a simple dominant to 

 two different recessives, and where one of these recessives also behaves 

 as a simple dominant to the other, the three characters concerned are 

 closely related physiologically. From this he argues that a given 

 factor is a complex thing which may undergo modifications affecting 

 its manifestation in the zygote without at the same time affecting its 

 allelomorphic distribution in gametogenesis. In the rabbit ca.se for 

 example the factor for self-colour, which we may denote by X, is 

 normally allelomorphic to itself As the result of some unknown 

 change in the constitution of the factor it loses the property of 



' Wilson (1913) has also advocated the hypothesis of MuHiple Allelomorphs in con- 

 uection with the Agouti-black rabbit. On his interpretation the factor X (=DE) always 

 turns a rabbit into a black or an agouti-black. This however is not in accordance with 

 fact, since the factor in question can be carried by a chocolate (cf. p. 44). 



