Hereditary Characters and their Modes of Transmission

Abstract

THIS volume deals very clearly and briefly with the whole field of heredity, but perhaps its most interesting feature is the development of a theory as to the relative share borne by the chromosomes and other parts of the sexual cells in the transmission of hereditary characters. Stated somewhat crudely, the theory and the arguments which support it are as follows:—In the chromosomes are represented new characters (i.e. individual variations, mutations, and the like), while other parts of the cell are concerned with the propagation of old-established racial characters. That the chromosomes do not bear entities representing all the inherited characters is shown, firstly, by experimental evidence, such as the fertilisation of enucleated Echinoderm ova. For instance, Godlewski fertilised enucleated eggs of sea-urchins with the sperm of crinoids and obtained gastrulæ which possessed pure maternal characters only. Second, through the reducing divisions half the chromatin is eliminated from the mature gametes. In spite of this, all the racial characters are shown by the individual which develops from the fertilised ovum. If one half the entities representing the racial characters of the father are absent from the sperm, it is so improbable as to be almost inconceivable that exactly those characters which are unrepresented will be supplied by the mother, seeing that the entities present in the ovum have been halved in number in a corresponding way. Hereditary Characters and their Modes of Transmission. By C. E. Walker. Pp. xii+239. (London: Edward Arnold, 1910.) Price 8s. 6d. net.