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INHERITANCE 



Thus in each of the six periods of the last four months, the parents 

 with high numbers of spines produced offspring with higher mean num- 

 bers of spines than did parents with low numbers of spines, though the 

 differences were not very great. 



Selective breeding of this type was practiced also with relation to the 

 length of the longest spines. The results here show clearly a phenomenon 

 of much interest, namely inherited variation with "regression toward the 

 mean" of the biotype as a whole. This appeared also in the results of 



Table 17: Inheritance of Spine Length, with Regression Toward 

 THE Mean, Difjiugia corona, Clone 326; Measurements of Spine 

 Lengths, in Units of 4 2/3 Microns Each (from Jennings, 1916) 



Mean length for all, 12. 54 



selective breeding with respect to other characters. The results of selection 

 for length of spines are given in Table 17. (The spines were measured 

 in units, each of which was 42^ microns.) 



Table 17 shows that parents with longer spines produce, on the 

 average, offspring with longer spines, so that there is a distinct tendency 

 to inheritance in spine length, even within the single clone. 



But another relation is equally evident. Parents that are above the 

 mean of the biotype (12.54) produce offspring that are above the mean, 

 buf not so much above the mean as are the selected parents. Parents that 

 are below the mean produce offspring that are below the mean, but not 

 so much below the mean as are the selected parents. That is, inheritance 

 of the parental peculiarities occurs, but always with regression toward the 

 mean of the biotype. On the average, the offspring diverge from the 



