What is the basic unit of chromatin formed by DNA wrapped around histones?

• A. Beads on a String
• B. Nucleosome
• C. Chromatid
• D. Chromosome

Answer: (B)

DNA wrapped around histones forms the nucleosome, the basic unit of chromatin. Each nucleosome consists of about 147 base pairs of DNA wound around a histone octamer (two copies of H2A, H2B, H3, and H4). Linker DNA connects successive nucleosomes, with the histone H1 helping the fiber fold. The beads-on-a-string picture describes this arrangement along the DNA. This unit is key because it regulates access to genetic information by controlling how tightly DNA is packaged. The other terms refer to larger structures or descriptive visuals: chromatids are replicated copies of a chromosome, chromosomes are highly condensed structures during cell division, and beads on a string is a way to visualize the nucleosome arrangement rather than a separate unit.