CHAPTER IV 



GENERAL CHARACTERISTICS OF THE MENDELIAN PHENO- 

 MENON ILLUSTRATED BY THE CASE OF THE 

 ANDALUSIAN FOWL AND THE INHERITANCE OF 

 EYE-COLOUR IN MAN 



I PROPOSE to give now some further instances of the 

 Mendelian hereditary phenomenon to illustrate some 

 of its general characteristics. One of the most 

 striking instances of the Mendelian phenomenon is 

 that which is exhibited by the breeding properties 

 of the Andalusian fowl. In perhaps no other case 

 is the contrast between what actually occurs 

 and what we expect to happen, seen in bolder 

 relief. 



The blue Andalusian fowl owes its popularity 

 with the public, and its interest to the student of 

 heredity, to its colour. This is a slaty blue-grey. 



If two birds of this strain are mated, it will 

 be found that they do not breed true. Besides 

 the blue birds which hatch out, there will also 

 be a certain number of blacks, and of whites with 

 occasional black points, hereafter to be referred to 

 simply as " whites." If the blues thus produced are 

 mated together, blacks and " whites " will again 

 appear amongst their offspring, and no amount of 

 breeding from the blues alone will rid them of the 



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