SOME BELIEFS OF PRACTICAL BREEDERS 575 
qualities to all his female offspring regardless of the genotypes of the 
females to which he is mated, whereas one of the genetie constitution 
(Zm)(Zm)ll would transmit low egg laying capacity to such an extent 
that among his daughters even from high producing hens none would 
fall in. the high producing class. For favorable characters the validity 
of this interpretation depends upon dominance of the determining factors, 
a condition by no means universally fulfilled. 
The Relative Factor Potency Interpretation.—There is some evidence 
that the potency of a given factor sometimes varies with the source from 
which it is derived. Pearl has suggested for example that the factor L 
when derived from the Cornish Indian Game has a lower absolute fecun- 
dity value than that of the same factor in the Barred Plymouth Rock. 
The suggestion amounts to an application of the hypothesis of multiple 
allelomorphism, a graded series of multiple allelomorphs of differing 
potencies, or different relations with respect to dominance, being con- 
ceived to determine the absolute degree of expression of the factors. We 
recall here Detlefsen’s work with the agouti factor of the wild Cavia 
rufescens which was recessive to the agouti pattern of the tame guinea- 
pig, and less decided in its phenotypic expression. The conclusions of 
Goldschmidt that races of the gypsy moth exist which have sex factors 
of various potencies, such that crosses between them give series of 
intersexual forms, while less definite with respect to the actual factors 
involved, provides some evidence in support of the belief that some of the 
phenomena of prepotency are dependent upon actual differences in the 
factors themselves. 
The Hereditary Complex Interpretation——The characters for which 
families are prepotent are evidently often complex, as for example 
speed in horses, total butter-fat production in dairy cows, beef con- 
formation in cattle, and so on. They must, therefore, depend upon 
a favorable genetic constitution with respect to series of factors. 
This interpretation is based upon the conception that factors form 
physico-chemical reaction systems and it follows the lines which have 
been developed in the application of this hypothesis to species hybrids. 
We have pointed out for instance that varieties of Nicotiana tabacum 
impress their total set of characters upon the hybrids with N. sylvestris 
because of the dominance of the tabacum reaction system. Certain 
characters which are recessive within the tabacwm group are expressed 
in such species hybrids apparently because of their interrelations with 
other factors in the tabacum group. This idea is also borne out by 
certain of the Drosophila experiments. Thus Morgan notes that the 
factor for truncate wings, usually recessive, is dominant in races which 
have the black factor. The hypothesis rests-upon a belief that sometimes 
factor interrelations determine whether a particular member of an 
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