Open main menu

Page:Popular Science Monthly Volume 81.djvu/376

This page has been validated.
370
THE POPULAR SCIENCE MONTHLY

will denote the presence of the ovary or the ♀ sex determiner. Then will denote the absence of femaleness and the absence of an ovary. Obviously a separate letter is not needed for this "anatomical factor," since the presence of an ovary is the objective criterion of the existence of the female sex, its absence of the existence of the male sex.

2. The "first production" factor. This is the primary physiological factor which in coexistence with makes the bird lay eggs during the winter period. Quantitatively it may be taken as determining a winter production of more than zero eggs and less than 30. The presence of this factor will be denoted by .

3. The "second production" factor. This is a second physiological factor, which in coexistence with and leads to high fecundity. The presence of this factor will be denoted by and its absence by the corresponding small letter. When and are present the addition of makes a winter production of over 30 eggs. If is present and absent the presence of leads to a winter production of under 30 eggs. Thus either or alone makes a record of 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 and are not qualitatively the same. That is, the increased production when and 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 present in a bird it does not make her a high producer. may be considered an excess production factor, which erects a superstructure on the foundation furnished by . In the absence of it lacks the foundation from which to start, and hence only can build about as high as would alone. Of course, it will be understood that in the presence of (absence of female sex and ovary) these physiological fecundity factors and are simply latent.

Using the letters in the manner defined above, and with the usual Mendelian method of writing gametic and zygotic formulæ, the data indicate that there exist 9 different types (in respect to fecundity) of Barred Plymouth Rock males, 6 types of Barred Plymouth Bock females, 3 types of Cornish Indian Game males, and 3 types of Cornish Indian Game females. The only point needing particular attention in reference to these formulas is that the factor , the excess production factor, behaves in inheritance as a sex-limited or sex-correlated character. It is repelled by the female determiner . It is thus like the barred pattern factor in the Barred Plymouth Rock fowl.[1] 3 In consequence gametes of the type are never formed. Any gamete which bears does not, under any circumstance, ever carry . All females

  1. 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.