Comparative study of human chromosome replication in primary cultures of embryonic fibroblasts and in cultures of peripheral blood leucocytes

Early and late replication of chromosomes in primary cultures of embryonic fibroblasts and in cultures of peripheral blood leucocytes were analysed using pulse and continuous incorporation of ³H-thymidine. In both types of cells chromosomes begin the synthesis period synchronously. The termination of the DNA synthesis of chromosomes is an asynchronous process and has peculiarities in every type of cells, chromosomes 1, 16, 21–22 are labelled relatively more intensively in fibroblast cultures than in leucocytes but the chromosomes of group 4–5, on the contrary, contain more grains in leucocyte cultures than in fibroblast cultures. It is highly probable that the discovered differences in late replication of the mentioned chromosomes in the investigated types of cells are connected with the differences in functioning of these chromosomes in the two different types of cell systems.