Patterns of pigmentation in experimentally produced mouse chimaerae

A General description of the development of mouse chimaerae and an account of the techniques for their production were given in previous reports (Tarkowski, 1961, 1963). The chimaeric character of the embryos and young obtained was tentatively claimed in the first of these publications because (1) the actual union of two eggs into one blastocyst was seen in culture in vitro, (2) of the occurrence of intersexes, (3) pigment synthesis of the types of the dark component occurred in the majority of individuals developed from pairs of eggs differing genetically in factors for pigmentation. The last criterion was met only by macroscopic search for pigment in the eyes. The present report gives a more detailed description of the distribution of pigment forming cells in these animals, based on histological analysis. Some remarks on the validity and applicability of such a criterion for estimating the degree of chimaerism were made at the 13th Annual Meeting of the Tissue Culture Association (Tarkowski 1963).