Polymorphism are used in paternity suits and forensic analysis. V. Packaging eukaryotic DNA into nucleosomes DNA is highly negatively charged due to the phosphate backbone. The repulsive action of the 'like' charges causes the DNA to be very stiff. Stiff DNA does not package well into tight spaces such as the nucleus. The solution is to neutralize the charge.
Histones are small, basic proteins that neutralize the charge.
Two copies of each associate to form a histone octamer. The basic charges form a track on the outside of the octamer that allows the DNA to wrap around. Nucleosomes are very stable on this curved DNA due to the tendency for the DNA to wrap around the histone octamer. Histone octamers not only function to condense DNA but also block access of regulatory proteins to specific DNA sites. Promoter DNA that is positioned within nucleosomes is not expressed.