When does DNA replicate actually? I read on Wikipedia that when the cell enters prophase during mitosis , the DNA has already been duplicated , that is the DNA is replicated in the chromatin form , but here I see the picture which shows the already condensed DNA ( now chromosome ) divide into sister chromatids. When does DNA divide actually ? !enter image description here!enter image description here link to wikipedia -<

According to This paper and most biology textbooks, S-phase or synthesis phase is literally defined by the beginning and ending of DNA replication. The first picture does not accurately represent the nature of DNA replication and is instead a model to help people track DNA copies during stages of cell division. DNA is replicated as chromatin and condenses to "double" chromosome form. You can see some micrographs of DNA condensation in this paper. You'll see that they don't condense as single chromatids, but they are already replicated.