228 MENDELISM 
But on turning to the dominant parent, the case is 
found to be different. For such an one may be either 
a pure dominant homozygote giving off A-gametes 
only, or it may be a heterozygote giving off equal 
numbers of A- and a-gametes. Yule shows that if both 
the parents of the A individual exhibited the character 
A, the proportionate number of its offspring which may 
on the average be expected to show the A character is 
greater than would have been the case if one of its 
parents exhibited the character a. And in a similar 
way a knowledge of the characters shown by the grand- 
parents adds something to the certainty of the pre- 
diction as to the proportionate numbers of offspring of 
the two kinds which are to be expected, when the 
average of a number of cases is taken according to the 
usual statistical method. 
Yule therefore regarded the case of the dominant 
character as showing conformity with the law of 
ancestral heredity, according to his own statement of 
that generalization, which was to the following effect : 
The law that ‘ the mean character of the offspring can be 
calculated with the more exactness, the more extensive 
our knowledge of the corresponding characters of the 
ancestry, may be termed the law of ancestral heredity.’* 
It may be remarked in passing that Yule’s dis- 
tinction of the problems of genetics into those of 
intra-racial heredity and those of hybridization cannot 
now be regarded as holding good, unless the term 
hybridization is to be extended to many cases—e.g., 
that of the inheritance of coat colour in thoroughbred 
* “New Phytologist,’ vol. i., p. 202. 
