Replication occurs in the interphase or S phase of the cell cycle and in the leptin subphase. Primitive cells contain circular DNA and have no ends or centers. Replication starts anywhere in the progenitor cell and replication forks move in both directions and meet at the midpoint. Replication of circular DNA is rapid and can add up to a million base pairs per minute. A cell’s circular DNA has two ends, and replication begins at multiple sites between the strands. Replication of circular DNA is slow and can add up to 500-5000 base pairs per minute. Replication of E. coli takes 20-30 minutes. Replication in animal cells takes 1.4-24 hours. Replication can start at 50,000 sites in Dosophila.