Chromosome sets and DNA content
DNA replication doubles DNA content without doubling chromosome-set ploidy.
Key knowledge
Ploidy counts sets of homologous chromosomes, whereas DNA content counts the amount of DNA. In a typical diploid mitotic cycle, a G1 nucleus is 2n, 2C; after S phase it remains 2n but is 4C because each chromosome has replicated into sister chromatids. Homologous chromosomes are the corresponding members of different sets; replicated sisters are copies of one chromosome.
Conditions and scope
- n denotes one chromosome set and C the DNA amount of one unreplicated haploid nuclear genome; report these per specified nucleus and cell-cycle stage.
- The example excludes endoreduplication, polyploidy and multinucleate accounting. Labels must be reconsidered when chromatids separate or nuclei divide.
Sources · 2
References
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Evidence and review
Inspected Biology §10.1 chromosome/ploidy definitions and NCERT §10.1.1's explicit S-phase 2C→4C with unchanged 2n. No fixed cell-cycle duration or universal chromosome architecture is inferred.
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