212 MENDELISM 



results in his memoir, ' On a Generalized Theory of 

 Alternative Inheritance, with special reference to 

 Mendel's Laws.' Pearson's treatment of the subject 

 involved advanced mathematical reasoning, and we 

 can, therefore, only give a brief summary of his main 

 results. Pearson proposes special terms for the A and 

 the a elements respectively of a couplet or pair of 

 allelomorphs. He proposes to call the A element a 

 protogene, and the a element an allogene, and he thus 

 distinguishes between the two sorts of homozygotes 

 by calling A A a protozygote and aa an allozygote. 



Pearson considered the case of a population breeding 

 together at random, in which a single measurable 

 character, such as stature, is determined by the combined 

 action of an indefinite number of pairs of allelomorphs, 

 and he proceeded to work out the value of parental 

 correlation which was to be expected under these 

 circumstances. This value he found to be exactly 

 one-third, a value which happens to be identical with 

 Galton's original determination of parental correlation 

 from his statistics of human stature. A considerable 

 number of determinations of parental correlation 

 have, however, since been made in the case of all 

 kinds of characters. The values show considerable 

 variation, but the average which they indicate is much 

 nearer to 0-5 than to 0*33. Pearson therefore con- 

 cluded that in none of these cases could anything 

 resembling Mendelian inheritance be taking place, 

 and that the latter is, in fact, the exception rather than 

 the rule. 



Mendelians, aware of the certainty of their own 



