However, under “resting” conditions (what cell biologists call the G₀ and G1 phases of the cell cycle), metaphase chromosomes are not visible, and the chromatin is allowed to loop away from the scaffold, loosely dispersed throughout the nucleus as heterochromatin. In some regions of the chromatin, the DNA is unwound from its spools of histone protein and is undergoing transcription into messenger RNA. And during the S phase of the cell cycle, long coils of chromatin called replication units are made accesible to DNA polymerase so the genetic material can be replicated, in preparation for cell division. We’ll talk about all of this in future issues.