Polycomb complexes are protein complexes involved in the regulation of development and were first identified in Drosophila melanogaster. The name is a description of the phenotype of the mutants of the first gene identified in this group, namely, polycomb (pc). All the genes coding for proteins that bring about similar phenotypic effect are said to belong to polycomb group and the proteins are called polycomb proteins. Homologues of these proteins are found across eukaryotes including humans. Polycomb complexes recognize sequences on the DNA and bind at sites referred to as polycomb responsive elements (PRE). There are different polycomb complexes with different proteins as partners in the complex, some of which bring about transcriptional repression through histone modifications (Ringrose and Paro 2004).