Biometrical genetics : the study of continuous variation / K. Mather.

  • Mather, Kenneth, 1911-1990.
Date:
[1949]
Catalogue details

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

Credit: Biometrical genetics : the study of continuous variation / K. Mather. Source: Wellcome Collection.

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    ê CHAPTER 1 THE GENETICAL FOUNDATION 1. biometry and genetics The growth of genetical science as we know it today began with the re-discovery of Mendel's work in 1900. Nevertheless, at the time of that event there were already genetical investigations in active progress; investigations which, although contributing relatively little to the development of genetical theory, still have an importance of their own. These were begun by Francis Galton, who published a general account of his methods and findings in Natural Inheritance (1889), and were continued by Karl Pearson and his pupils. From them the application of statistical mathe¬ matics to biological problems received a great impetus, and if for this reason alone they mark a significant step in the growth of quantitative biology. The relative failure of this work in its avowed purpose, that of elucidating the relations of parent to offspring in heredity, stems from a variety of causes. Mendel himself regarded the failure of his predecessors as due to their experiments not making it possible 'to determine the number of different forms under which the off¬ spring of hybrids appear, or to arrange these forms with certainty according to their separate generations, or definitely to ascertain their statistical relations'. While Galton's work can hardly be regarded as failing in the third respect, the nature of the material he chose rendered it impossible for him to succeed in the other two. His extensive use of human data, with its small families and genetically uncertain ancestries introduced difficulties enough; but it was the choice of metrical or quantitative characters, like stature in man, that foredoomed the work from the point of view of the laws of inheritance. These characters show continuous gradations of expression between wide extremes, the middle expression being most common in any family or population, and the frequency of occurrence falling away as we proceed towards either extreme (see Fig. 2). The distributions of frequencies of the various grades of expression sometimes, as with stature in man, approximate closely to the Normal curve; but while retaining the same general shape they depart in other cases from this precise form, for example by being asymmetrical. The simple Mendelian 1