During prophase (of mitosis), a human cell contains 46 replicated chromosomes — the same number of chromosomes as before replication, because DNA replication during the preceding S phase duplicates each chromosome's DNA but does not change the chromosome count.
Here's why the number stays at 46 rather than doubling to 92: during S phase, each of the 46 chromosomes is copied, producing two identical sister chromatids joined together at a centromere. This pair of sister chromatids is still considered a single chromosome (just in duplicated form) until they separate. Separation doesn't happen until anaphase, when the sister chromatids are pulled apart and each chromatid becomes its own independent chromosome. At that point, the cell briefly has 92 chromosomes (46 going to each pole), which then become the 46 chromosomes in each of the two daughter cells after cell division completes.
So to summarize the chromosome count through mitosis for a typical human somatic cell:
- Before S phase (G1): 46 unreplicated chromosomes (single chromatid each)
- After S phase, through prophase, prometaphase, and metaphase: 46 replicated chromosomes (each made of two sister chromatids, for a total of 92 chromatids)
- Anaphase onward, and in each daughter cell: 46 unreplicated chromosomes again
The number 46 is specific to humans; other species have different chromosome numbers, but the same logic applies universally — the chromosome count doesn't change during replication or through prophase, metaphase, and prometaphase, because sister chromatids are counted as one chromosome until they physically separate at anaphase. This is a key concept that's often confused with the difference between chromosome number and DNA content (which does double after replication, even though chromosome number does not).