The nucleus constitute DNA-protein complex termed chromatin. Chromatin is simply DNA double helix entwined around proteins referred to as histones. These appear like beads when stretched out, and each “bead” (DNA and histone) form the nucleosome. Genes are hereditary materials found on DNA. Chromosomes are composed of closely-packed chromatin, and become clearly visible under a microscope during mitosis. During this stage the chromosomes have undergone the S Phase of the cell cycle, hence a copy of the DNA has been synthesized by DNA polymerase.
