46 FECUNDITY IN THE DOMESTIC FOWL 



It is evident that selection within the line here was quite without effect. 



Another example of the same thing from line D31D447 may be given by 

 way of further illustration. In this line there was in the F : generation a 

 family of ten daughters. Of these some were very good and some were poor 

 layers. All were bred. The mean results are shown in the next table. 



EFFECT OF SELECTION OF GOOD AND POOR WINTER LAYERS IN THE SAME LINE, 0310447 



Generation F, F2 FS 



Mean winter record of good layers and their progeny 62.5 23.75 22.00 



Mean winter record of poor layers and their progeny 32.0 28.75 I 4-75 



Here again it is plain that selection within the line was without effect. 

 Many more examples of the same sort might be given from the records did 

 space permit. In general there is no evidence whatever that the selection 

 of individuals of different laying records, but belonging to the same fecun- 

 dity genotype, produces any definite or permanent effect whatever. 



DISCUSSION AND CONCLUSIONS 



Taking into consideration all the facts which have come out of this 

 study, one is led to the following view as to the composition of a flock of 

 fowls in respect to fecundity. In the average flock we may presume that 

 there will probably be represented a number of fecundity genotypes, some 

 high, some low, and some intermediate or mediocre. In an ordinary flock 

 these genotypes will be greatly mixed and intermingled. Further, the 

 facts in hand indicate that the range of variation in fecundity within the 

 genotype is relatively very large, nearly as great, in fact, as in the general 

 population. Thus while fecundity genotype means may be and usually are 

 perfectly distinct, there is much overlapping of individuals in the different 

 lines. In consequence it results that the egg record of an individual bird 

 is of almost no value in helping to tell in advance of the breeding test to 

 what fecundity genotype it belongs. Essentially this same fact has been 

 brought out in all of the work which has been done with pure lines. The 

 only difference in the present case lies in the fact that the range and degree 

 of variation within the line appears to be relatively greater in the case of 

 fecundity than in the case of most characters hitherto studied, as, for 

 example, size relations in beans or Paramecium. 



The most serious difficulty which confronts one in the attempt to analyze 

 the inheritance of a character like fecundity lies in the almost inextricable 

 mingling of genotypes in the great majority of individuals. This, of 

 course, is a direct consequence of the manner of reproduction .The germ 

 plasm of two separate individuals must unite to form a new individual. By 



