Final answer:
During DNA replication in the S phase, the DNA is in the form of chromatin, which allows for easier replication. After replication, the sister chromatids are held together at the centromere by cohesin proteins.
Step-by-step explanation:
During the S phase of DNA replication, the DNA is in the form of chromatin. Chromatin is a complex of DNA and proteins that makes up the contents of the nucleus of a cell. It is the default form of DNA in the nucleus, where it is organized and condensed into a more compact structure.
The reason why DNA is in the form of chromatin during S phase is because it allows for easier replication. Chromatin allows the DNA to be accessible for the enzymes involved in DNA replication, such as DNA polymerase. The enzymes can easily access the DNA and copy it to produce two identical copies-sister chromatids.
After DNA replication is complete, the sister chromatids are held together at the centromere by the protein complex called cohesin. This ensures that the two copies of the DNA stay together until they are separated during cell division.