BEGINNING with a short statement of corpuscular theories of the germ-plasm, the author classifies chromosomal aberrations into changes of (a) the number of chromosomes, (b) the number of genes in a chromosome, (c) the linear order of the genes. The bar-eye genes of Drosophila is then discussed on the basis of gene duplication. Other topics considered are (1) the relation between a chromosome break and the dominance of the neighbouring genes, (2) visible mutations appearing at the point of breakage, and (3) reversibility of the position effect. It is concluded that the existence of a position effect is proved. The functioning of a gene is therefore determined not only by its own structure but also by that of neighbouring genes. A gene can therefore be modified by its transfer to a new position, arid the position effect can be used in order to investigate the first stages of the action of a gene in development.
Exposés de génétique
2: L'Effet de position et la théorie de l'hérédité. Par Prof. Th. Dobzhansky. (Actualités scientifiques et industrielles, 410.) Pp. 38. (Paris: Hermann et Cie., 1936.) 12 francs.