Cellular DNA and epigenetics. Illustration of the packaging of deoxyribonucleic acid (DNA) and associated epigenetic factors. DNA in the cell nucleus winds tightly into coils that wrap around proteins called histones. Further coiling forms strands of chromatin, which condenses during cell division to form structures called chromosomes (x-shaped). Epigenetic factors are those that affect how genes are processed and used by cells (transcription). Examples shown here are methyl groups (blue crystals, lower right) and histone tails (upper right). Methylation of histones affects transcription of genes. For this artwork without labels, see image C027/0577.