 Whereas mutant cell lineages arise as a change in the sequence of standard bases, epigenetically altered cell lineages retain the sequence of standard bases but have gene sequences with changed levels of expression that can be passed down to subsequent cell generations.Epigenetic alterations include methylation of CpG islands of a gene promoter as well as specific chromatin histone modifications.Faulty repair of chromosomes at sites of DNA damage can give rise both to mutant cell lineages and/or epigenetically altered cell lineages.