Full text: papers communicated to the first International Eugenics Congress held at the University of London, July 24th to 30th, 1912

54Section I.R. Pearl. 
L2 makes a winter production of over 30 eggs. If F is present and Lx 
absent the presence of L2 leads to a winter production of under 30 eggs. 
Thus either Lx or L2 alone makes a record of under 30 eggs. They are 
independent determiners of this degree of production. It should be pointed 
out, however, that in spite of their equivalence in this regard the factors 
Lx and L2 are not qualitatively the same. That is, the increased production 
when Lj and L2 are both present, is not because there are present two 
“ doses ” of the same determiner. The proof of this is found in the fact 
that when there are two “ doses ” of Lx present in a bird it does not make 
her a high producer. L2 may be considered an excess production factor, 
which erects a superstructure on the foundation furnished by Lr In the 
absence of Lx it lacks the foundation from which to start and hence only 
can build about as high as Lx would alone. Of course, it will be under­ 
stood that in the presence of f (absence of female sex and ovary) these 
physiological fecundity factors and L2 are simply latent. 
Using the letters in the manner defined above, and with the usual 
Mendelian method of writing gametic and zygotic formulae, the data 
indicate that there exist nine different types (in respect to fecundity) of 
Barred Plymouth Rock males, six types of Barred Plymouth Rock females, 
three types of Cornish Indian Game males, and three types of Cornish 
Indian Game females. The only point needing particular attention in 
reference to these formulae is that the factor L2, the excess production 
factor, behaves in inheritance as a sex-limited or sex-correlated character. 
It is apparently repelled by the female determiner F. It is thus like the 
barred pattern factor in the Barred Plymouth Rock fowl.* In consequence 
gametes of the type FL2 are never formed. 
Any gamete which bears F does not, under any circumstances, ever 
carry Z2. All females which carry the excess production factor L2, are 
heterozygous in respect to it. 
We have fecundity practically determined, then, by two physiological 
factors, one of which is sex-correlated in its inheritance and the other not. 
The accordance between observed fact and theoretical expectation on this 
interpretation of the results is shown in the following tables which give the 
results of a portion of the actual experiments. As the experiments were 
rather extensive it is not possible here to present anything like the complete 
material. Only representative matings are here given. Table II. gives the 
results of some of the Barred Plymouth Rock by Barred Plymouth Rock 
matings in detail, in order to show, not only the accordance between 
observation and theory, but also the distinctness of the classes of fecundity 
segregated (shown by the average winter production in each segregated 
class).* cf. Pearl, R. and Surface, F. M. Arch. f. 
Entwick. Mech. Bd. XXX, pp. 45-61, 1910, 
and Science, N.S. Vol. XXXII, pp. 870-874, 1910.
        

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