In eukaryotes, regulation of gene expression can be controlled by tight or loose packaging of genes in chromatin(DNA & histones). The structure of chromatin can be altered by various types of modifications in DNA and Histones such as methylation, acetylation, phosphorylation, etc. Various chromatin modellers also help in altering the structure of chromosomes. The compaction of DNA in the form of chromatin limits gene accessibility for transcription factors. Different modifications like nucleosome sliding, histone eviction, histone replacement modify the chromatin structure and make it available for gene expression.