Initiation of DNA replication in human chromosomes

DNA replication within the first 10 min of the S phase was studied using synchronized human diploid cells. It appeared that every chromosome in the human genome, including late-replicating X, had segment(s) which initiated DNA replication within the first 10 min of the S phase. The position, the shape and the size of these segments corresponded to those of Q(G)-negative bands suggesting that each of them constitutes a basic unit of initiation of DNA replication.