Practice question

Replication timing correlates tightly with chromatin state and transcriptional activity. Euchromatin, being open, acetylated and gene rich, replicates early in S phase when dNTP pools high and origin recognition complex easily loads. Constitutive heterochromatin, highly condensed with H3K9 trimethylation, HP1 oligomers, late-firing origins and peripheral nuclear lamina anchoring, replicates late in S phase. Autoradiography using tritiated thymidine and modern Repli-seq show satellite DNA incorporates label late. Facultative heterochromatin replicates mid to late, but constitutive blocks representing centromeric satellites replicate latest ensuring structural domains duplicated after coding regions.