BY RAYMOND PEARL 43 



The facts here briefly discussed are shown in the following table and 

 graphically in Fig. 4. 



It is apparent from the table and the diagram that the main line and the 

 "mutant" line are entirely distinct. Indeed they do not overlap in their 

 ranges even excepting only the pathological individual G495. The 

 "mutant" pullet E248, for some reason or other, possessed the capacity 

 both to lay a relatively large number of eggs, and the genes necessary to 

 make this quality appear in her progeny. Whether this individual is to be 

 regarded as a true "mutation" would appear to be largely a question of 

 definition. In the writer's opinion the most probable explanation is that 

 E248 is a Mendelian segregation product. That is, let it be supposed that 

 both D168 and D61 were heterozygous with respect to degree of fecundity, 

 and were producing in some (unknown) ratio both "high fecundity" and 

 "low fecundity" gametes. Then E248 may be supposed to have originated 

 from the union either of two "high fecundity" gametes or one high and one 

 low fecundity gamete. She then would be either a DD or a DR bird, on 

 the assumption, which the facts seem to support, and which I have more 

 fully discussed elsewhere, 12 that high fecundity is dominant over low. 



The subsequent breeding history of E248 indicates that it was probably 

 a DD bird, though the reasons for this opinion can not be fully gone into 

 here. The general view, recently emphasized by Nilsson-Ehle, 13 that 

 phenomena of mutation are, in many cases at least, merely cases of Mende- 

 lian segregation has much evidence in its favor. 



The pedigrees which have been given are merely illustrations. Many 

 other similar ones might be cited from the records in hand did space permit. 

 In the experiments during the last three years the attempt has been made 

 to propagate separately lines of high, medium and low fecundity. In the 

 course of this work it has been found that lines of high fecundity were nearly 

 if not quite as likely to have originated with individuals of a low record of 

 production as with those of a high record. Similarly, many low fecundity 

 lines have originated with individuals which were themselves exceedingly 

 high layers. Indeed one of the highest winter layers which have ever 

 appeared in the stock evidently belonged to a genotype of very low fecun- 

 dity, since it has never been able to produce progeny of anything but the 

 poorest laying capacity. The breeding history of this bird (D352) is indeed 

 so interesting that it may be briefly discussed here. This bird in her pullet 

 year laid 98 eggs between November 10 and March 1 and made a record for 



12 "Inheritance in 'Blood Lines' in Breeding Animals for Performance, with Special 

 Reference to the '2OO-egg' Hen," Rept. Amer. Breeders' Assoc., Vol. VI, 1911. 



13 Nilsson-Ehle, H., "Kreuzungsuntersuchungen an Hafer und Weizen," Lunds Univ. 

 Arsskr., N. F., Aid. 2, Bd. 5, Mr. 2, 1909, pp. 1-722. 



