THE 'CYTOGENETICS' OF BLACK AND WHITE GUINEA PIG SKIN

Abstract

IT is an obvious empirical fact that the differentiated cells of the adult organism, if they are capable of dividing at all, 'breed true' and preserve for ever in cellular inheritance their specificity of histological type. Even under the regime of tissue culture, in which a cell lineage may well comprise a hundred generations, there is' no reduction of embryological rank, and no degradation of histological specificity that is not a mere matter of 'nurture' and reversible oat will. What is the mechanism of conservative inheritance in the cell lineages generated by mere asexual fission ? An attempt will be made to answer this question by special reference to two cytogenetically distinct but closely related types of cell : those of the 'white' and 'black' epidermal epithelia of guinea pigs' skin. It will be suggested that the inherited difference between them is due to the possession by the black epidermis of a cytoplasmic self-reproducing system concerned with melanogenosis that has some of the properties of what are usually called 'viruses'. Analysis of the type we have undertaken is, indeed, only made possible by the circumstance that black skin is capable of 'infecting' white, and endowing it with its own cellular phenotype ; a process which is in some respects analogous to a cross between sexual organisms, and which has the same methodological significance for the study of cellular heredity as the phenomenon of segregation has for Mendelian genetics.