Studies on Spotting Patterns III. Interaction between Genes Affecting White Spotting and Those Affecting Color in the House Mouse.

REVIOUS papers in this series (DUNN and CHARLES 1937; DUNN P 1937) have described the interactions occurring among a number of mutant genes which determine various white spotting patterns of the house mouse. The most noticeable effect of these genes is to suppress the development of color in certain areas of the pelage. The coat colors of mammals are due to pigments produced in the epidermis and laid down in the developing hair. These pigments, so far as is known, are all melanins and are produced by one type of process, the oxidation of a colorless chromogen to a pigment. This reaction in invertebrates is catalysed by the enzyme tyrosinase, and a similar reaction probably occurs between tyrosin and tyrosinase in the skins of pigmented vertebrates (ONSLOW 1915; PUGH 1933). I t is probably a process of this sort which is interfered with in certain areas by the action of the genes which affect white spotting. The variations in coat colors which appear in mice are due to the nature of the melanins and their distribution in the hair; and the underlying processes are controlled by genes which probably determine, among other things, the stage to which the oxidation process is carried. By mutations in such genes and by their interactions the familiar coat color varieties of mice have arisen; gray or agouti (the wild type), black, brown, yellow and many others. Since different processes occur under the influence of the different color genes, it is natural to inquire whether all of these processes are modified in a similar way and to a similar degree by the spotting genes.