An Exception to Mutual Exclusion of the Ciliary Antigens in Paramecium Aurelia.

HE system of ciliary antigens of Paramecium aurelia has provided abundant T material for the study of the inheritance of diverse phenotypes by organisms of identical genotype. Each animal of any one stock of P. aurelia has the genetic potential for the expression of a series of serologically different alternative ciliary antigens (SONNEBORN 1948, 1950a; SONNEBORN and LESUER 1948; BEALE 1954). Single genes have been shown to control the serological specificities of each of the antigens. Allelic genes have been found to control the specificities of serologically corresponding serotypes of different stocks of variety 4, in all cases thus far investigated (SONNEBORN 1950a, 1951; BEALE 1954). Normally only one antigen is detectably present a t any one time in a single animal. The identity of the antigen present on the cilia of an animal is referred to as its ciliary antigenic type or serotype. Serotypes can be inherited through varying numbers of vegetative and sexual reproductions. SONNEBORN and LESUER (1948) have shown that the cytoplasm plays an important role in serotype inheritance, by crossing serotypically different clones of the same stock. If no cytoplasm was exchanged the lines of descent from the exconjugants retained the serological differences of the conjugants, despite the fact that they must have become genically identical. However, if large amounts of cytoplasm are exchanged, often the lines of descent from both exconjugants of a pair have the same serotype, sometimes that of one exconjugant and sometimes that of the other. Which serotype will be expressed is determined by the interaction of the genes controlling the specificities of the different antigens and various factors such as temperature and growth rate (SONNEBORN 1947, 1950a; BEALE 1948, 1954; SKAAR 1952; SONNEBORN, OGASAWARA and BALBINDER 1953; MARGOLIN 1955). Changes in these factors, without any change in genotype, may cause transformations from one serotype to another. During the period of transition, usually lasting only about one to two fissions, it is often possible to detect as present a t the same time, both the disappearing initial serotype and the new serotype coming to expression (BEALE 1948, 1954; MARGOLIN 1955). Normally this is the only time a t which two different antigens, whose specificities are controlled by nonallelic genes, are to be found detectably present a t the same time in a single animal.