The inheritance of complex growth forms, such as stature, on Mendel's theory / By John Brownlee.

  • Brownlee, John, 1868-1927.
Date:
1911
Catalogue details

Licence: In copyright

Credit: The inheritance of complex growth forms, such as stature, on Mendel's theory / By John Brownlee. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    Arranging these as before, we find for blended inheritance the following- groups :— x4, 4 xAy, 6x2y2, 4 xy3, y4, and for mixed dominant inheritance, x4 + 2 x3y, 2 xAy + 6 x2y2 + 2 xy3, 2 xy3 + y4. If y = 2x the latter reduce to 5, 44, 32, so that the ultimate population is given by (5 + 44 + 32p where p is the number of double pairs originally present in either parent. This case is obviously asymmetric, but with p large quickly approaches symmetry. It is not, however, necessary to assume that two races mix. In each race diverse pairs must necessarily exist. It is possible that these may appear in proportions sensibly obeying the normal law. This, however, makes no difference in the preceding theory. Variation of individuals will but tend to smooth the curve (see note). Asymmetry also arises if the number of dominant elements from each race is unequal. If the hypotheses above discussed are granted, two points emerge demanding consideration :— (1) How far does this grouping accord with the observed statistics ? (2) How far does the grouping permit of the correlation coefficients found by observation ? (1) Every large series of statistics of a population give groups to which Type IV. corresponds better than the normal curve. Those of Pearson,* Powys,f etc., may be taken as types. In the case of the diagrams given by the former, it is very noticeable that at the apex the statistics give a value in excess of that shown by the normal curve fitted to the statistics, and at the limits there is a defect on the part of the statistics resembling that just found theoretically. With the curves of the Scottish insane given by Tocher J the same is also found. (2) With regard to the values of the correlation coefficients we are on firm ground. As we have seen, the hypothesis of blended inheritance leads to correlation coefficients as follows :— Parent and offspring ..... *5 ,, „ grand-offspring .... -25 ,, ,, great-grand-offspring . . . ‘125 ,, „ great-great-grand-offspring . . ’0625 * Pearson, “ On the Laws of Inheritance in Men,” Biometrika, vol. ii. p. 357. t Powys, “Data for the Problem of Evolution in Man,” Ibid., vol. i. p. 30.