How do we know that dna replication occurs during interphase, not early in mitosis? how do we know that dna replication occurs during interphase, not early in mitosis? the initiation and completion of dna synthesis can be detected by the incorporation of labeled precursors into dna. dna content in a g2 nucleus is twice that of a g1 nucleus. the initiation and completion of dna synthesis can be detected by the incorporation of labeled precursors into dna. dna content in a g1 nucleus is twice that of a g2 nucleus?