Most eukaryotic cells only express 20-30% of the genes they possess. The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state. Which histone modification directs the formation of the most common type of heterochromatin?
(a) H3 lysine 4 methylation
(b) H3 lysine 9 methylation
(c) H3 lysine 14 methylation
(d) H3 lysine 27 methylation
Answer: B