Final answer:
After DNA replication in the S phase but before M phase, each chromosome consists of two identical sister chromatids joined at the centromere, waiting to be separated during mitosis to ensure each daughter cell receives an identical set of chromosomes.
Step-by-step explanation:
When labeled deoxyribonucleotides are added to a culture of dividing cells, during the DNA replication process in the S phase of interphase, each chromosome is duplicated to produce two identical copies, known as sister chromatids. These sister chromatids remain joined together by a region called the centromere. The outcome of this replication event is a doubled amount of DNA within the cell, establishing the necessary conditions for each daughter cell to receive a full complement of genetic material during the subsequent M phase, or mitosis.
Reflecting on the cells after DNA replication but before M phase, we can affirm that each chromosome consists of two sister chromatids joined at the centromere. The cell has yet to enter mitosis, wherein these sister chromatids will be separated into two new cells. It is also necessary to mention that at this point, the cell is still in the final stages of interphase, preparing for the crucial mitotic phase. This preparation ensures that during cell division, a precise genetic duplication is distributed to the new daughter cells.