Practice question

Constitutive heterochromatin stays condensed throughout cell cycle, lacks protein-coding genes and replicates late in S phase. Molecularly it consists of tandem repetitive satellite DNAs clustered at centromeres, telomeres and secondary constrictions, such as alpha satellite, Satellite III and minor satellites. These repeats bind SUV39H1 methyltransferase generating H3K9 trimethylation that recruits HP1 oligomers and DNMT3B for DNA methylation, enforcing silencing and suppressing recombination. It forms visible chromocenters and provides structural roles in sister cohesion and segregation rather than encoding active transcripts, permanently repressed in all cell types.