Practice question

Core histones H2A, H2B, H3, H4 display remarkable conservation, especially H4 and H3 under strong purifying selection. Linker histone H1 exhibits greatest divergence, with multiple somatic subtypes H1.1 through H1.5, testis-specific H1t, H1T2 and oocyte-specific H1oo in mammals, differing greatly in C-terminal lysine-rich domain length and net charge. Subtype composition varies by tissue, differentiation and cell cycle phase, influencing linker DNA entry exit angle and degree of chromatin condensation. Sequence diversity enables specialization in compaction and transcriptional repression, contrasting highly constrained core histones required for octamer stability.