Human histone variants. (a) Complete list of human histone variants. Histone H2A variants consist of the highest number of variants (11) while histone H4 has only one variant reported to date in human cells. (b) Human histone H2A variants. Comparison of histone H2A variants with core H2A genes. Number of genes, gene names, protein size in amino acids and percent identity of variants to core H2A, along with key features of each variant, are provided. Note that H2A.Z.2.1 and H2A.Z.2.2, as well as macroH2A.1.1 and macroH2A.1.2, are splice variants of the same gene.