FERTILISATION 195 



quently drew the conclusion that the mechanism of inheritance 

 in the Andalusian fowl is comparable to what Mendel supposed 

 to exist in his hybrid peas. The gametes of the breed, according 

 to this hypothesis, instead of being ah 1 similar and carrying the 

 blue character (as one would suppose on Weismann's theory), 

 are of two different kinds, those of the one kind being bearers 

 of the black character, and those of the other being bearers of 

 the splashed-white character. Such gametes, uniting by chance 

 when the fowls mate together, give rise to three kinds of off- 

 spring, one black-white (becoming blue, actually, like the 

 parents), one black-black, and one white- white, these ap- 

 pearing (on an average) in the proportion of 2 : 1 : 1 according 

 to the law of probability. In this particular case of Mendelian 

 inheritance, neither of the two alternative parent characters 

 (i.e. neither black nor splashed-white) is dominant and neither 

 is recessive. Why black-bearing gametes uniting with white- 

 bearing gametes should give rise to blue individuals the 

 Mendelian theory does not attempt to explain. 



The importance of Mendel's discovery lies in the fact that 

 it forms the basis of a theory whereby variability can be dis- 

 cussed in terms of the conjugating cells themselves, and not 

 merely in terms of the resulting zygotes. Moreover, it is a 

 theory which has been found to be applicable to a very wide 

 class of facts. There are reasons for supposing that sex is a 

 Mendelian phenomenon ; that is to say, that the ova and 

 spermatozoa are themselves sexual entities prior to conjugation 

 (see p. 633). It still remains to be proved, however, that the 

 principles underlying Mendel's theory are applicable to all 

 forms of inheritance. 1 



It has been mentioned that on Weismann's hypothesis 

 every gamete contains ids representing both its parents and all 

 its immediate ancestors. On the other hand, according to the 

 Mendelian theory, although all the essential characters of the 

 organism are represented in each germ cell, the Mendelian 

 characters, or allelomorphs as they are called, are each repre- 

 sented by paternal or maternal ids only, and not by both, 

 while the immediate ancestors have no representation at all. 



1 Cf. Darbishire, "Recent Advances in Animal Breeding," Royal Horti- 

 cultural Society's Report of the Conference on Genetics, London, 1907. 



