DNA Structure and Replication

ID #1719

If the most condensed form of the chromosome (the X-shaped structure) contains two identical sister chromatids, why is it considered to be one molecule of DNA?

Actually, I don't think it would commonly be referred to as a single molecule, for reasons you just mentioned. It is, however, referred to as "a mitotic chromosome," despite the fact that it's actually two identical molecules of chromatin. We do this to avoid the confusion of changing chromosome numbers depending on the phase of the cell cycle. For example, humans are always referred to as having 46 chromosomes in our non-sex cells, even though technically we have 92 separate molecules after replication is complete. It just keeps the numbers easier to remember.

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