BY RAYMOND PEARL 



01-02 02-03 03-04 



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04-05 05-06 

 LAY I NO YBAK 



-09 0-10 



FIG. 5. Showing the effect of selecting high and low fecundity on a geno- 

 typic basis. The solid line denotes means of all " high lines " ; the dotted line 

 means of all " low lines." Up to 1907-08 the attempt had been to increase egg 

 production by breeding merely from the highest layers, regardless of pedigrees. 

 In 1907 and subsequent years the attempt has been to isolate genotypes of high 

 and low fecundity which shall breed true, each to Its own type. 



The results indicate the effectiveness of this method of selection. It 

 should be understood, of course, that only those pedigree lines are included 

 in the high line averages which uniformly in each generation show high 

 fecundity. A similar consideration applies to the low line averages. 



Let us now consider briefly the question of the effectiveness of selection 

 within the genotype. According to the "pure line" concept we should 

 not expect selection of high or low individuals belonging to the same geno- 

 type to produce any effect, except in cases where segregation has occurred 

 and the selected individuals are really gametically different, though having 

 the same pedigree. An example of this sort has been given in the case of 

 line D61D168 (cf. p. 331, supra). The ineffectiveness of selection within 

 the line when something of this sort does not occur is illustrated by line 

 D56D407. In the F x generation in this line there were four birds, of which 

 three were good layers and one was a poor layer. Two of the good layers 

 and the poor layer were bred. Large families were reared in F 2 and F 3 . 

 The average results in the three generations are given in the following table : 



EFFECT OF SELECTION OF GOOD AND POOR WINTER LAYERS IN THE SAME LINE, 0560407 



Generation F 1 Fz Fa 



Mean winter record of good layers and their progeny 76.0 46.7 35-57 



Mean winter record of poor layers and their progeny 26.0 52.0 36. 75 14 



14 If one family of four birds, which ought not in fairness to be included here be- 

 cause they were extremely inbred (brother-sister mating) in connection with another 

 experiment, is excluded, this average becomes 49.0. 



