Mendel's principles of heredity / by W. Bateson.

  • Bateson, William, 1861-1926.
Date:
1930
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Mendel's principles of heredity / by W. Bateson. Source: Wellcome Collection.

    177/470 (page 143)
    vili] Stibtraction-Stages 143 substances, say the chromogen, is distributed over the whole surface, but in the Dutch-marked, for example, it is reduced in quantity. The reduction however occurs in a fairly definite way, leading to the formation of a type having a recognizably distinct pattern. It does not seem an un¬ reasonable speculation to suppose that we have here to deal with a condition in which the amount of the substance is insufficient to cover the whole region which it occupies in the self-coloured type, though why it should be restricted to one special region more than another it is impossible to say. If the definite pied phases are to be thus regarded as representing quantitative diminution in the development of one of the determining substances, we may make a similar supposition in regard to the diluted colorations already mentioned in the case of mice. In the diluted colours the reduction in quantity, instead of diminishing the coloured area while keeping the intensity of the colour, is effected by diminishing the intensity of the colour while the totality of the distribution is retained. The black Dutch-marked mouse may thus be imagined to be a mouse in which one of the colour-factors exists in its full intensity, though there is not enough of it to cover the skin, while in the blue mouse the factor is generally distributed over the skin but in a dilute condition. In both cases alike the subtraction-stage as we may call it is a fairly definite stage in the reduction of the amount of pigment- A physical analogy—doubtless imperfect, but neverthe¬ less instructive—may be drawn from the way in which various oils distribute themselves over the surface of a liquid with which they do not mix, some forming circum¬ scribed patches of greater thickness, which may be compared with the patches on the Dutch rabbit, others spreading in a thin layer over the whole surface, like the dilute colours spread over the whole coat. The analogy breaks down at the fact that in the oils the physical distinctions to which the different behaviours are due cannot be transferred from one oil to the other, whereas in the rabbit this is accomplished—a fact which entitles us to represent the several properties as distinct and transferable factors. Thus the results of the cross between a black-and-white Dutch-