To get a more physical view of what's going on with DNA, and molecular genetics go here:
http://upload.wikimedia.org/wikipedia/commons/4/4b/ Chromatin_Structures.png
Blow the figure up enough to read the labels.
The words chromatin structure or chromatin template includes all of the above. On the far right we start with a DNA strand double helix coil.
Notice the words ``Add core histones''. Histones are small protein molecules that have a charged exterior that attaches to a section of the double helix. They create beads on the string and these units are called Nucleosomes. There are not a single wrap as shown, but usually multiple wraps.
Histone H1 also has an electrically charged surface and it activates the histone to rotate, stick together into the slack of histones with a DNA string wrap. The histone disks rotate and pull together into unit stacks.
The next packing step, ``add further scaffold proteins'' isn't well illustrated. The unit stacks leave unwrapped DNA strings between them. These strings and stacks are wrapped around the filament scaffold proteins in snake like fashion to form a snake bracelet. On electro-chemical activation the scaffold filaments constrict together to form an irregular shaped column. The column is the chromosome.
During RNA transcription, sections of this column are unwrapped, and exposed DNA strands are transcribed. This transcription process, includes opening an exposed DNA strands, encoding the RNA template, then putting single DNA strand back together, then re-attaching the base pairs to form the double helix.
Although the illustration shows DNA as a strand, this is a simplification. The double strand is further looped together in segmented fashion by external binding proteins to form loops and clumps. In addition there are variously shaped attachments on the outside rim of the strand. One class of such attachments are referred to as DNA methylation. There are also attachments to the histone nuggets the DNA is wrapped around.
Go here for the picture of attachments to DNA and the Histone:
http://upload.wikimedia.org/wikipedia/commons/4/4b/ Chromatin_Structures.png
These attachments compose part of the epigenome. They technically are not part of the DNA code itself, but they suppress and modify or alter the activity of the RNA transcription process---just as if they were part of the DNA code.
Here is the website that goes with the illustration:
http://upload.wikimedia.org/wikipedia/commons/4/4b/ Chromatin_Structures.png
It will tie together the Swedish historical study of the progeny of both boys and pregnant girls/women who experienced periods of famine.
CG