Final answer:
The nucleosome is the fundamental repeating unit of chromatin, consisting of DNA wrapped around an octamer of histone proteins, giving a 'beads on a string' appearance.
Step-by-step explanation:
The basic repeating unit of chromatin is the nucleosome, composed of DNA wrapped around an octamer of histone proteins. Histones are evolutionarily conserved proteins that are rich in basic amino acids, forming an octamer with two molecules each of histone types H2A, H2B, H3, and H4.
The DNA is then wrapped tightly around this histone core forming the nucleosome, which appears like a bead on a string when viewed as part of chromatin. Between nucleosomes, there is linker DNA that connects them together. During cell division, this chromatin condenses into chromosomes, which are organized structures of DNA and proteins.