Extrachromosomal DNA DNA in a variety of different organisms. Extrachromosomal DNA Extrachromosomal DNA is any DNA that is found outside the nucleus of a cell. It is also referred to as extranuclear DNA or cytoplasmic DNA. Most DNA in an individual genome is found in chromosomes but DNA found outside the nucleus also serves important biological functions. In prokaryotes, nonviral extrachromosomal DNA is primarily found in plasmids whereas in eukaryotes extrachromosomal DNA is primarily found in organelles. Mitochondrial DNA is a main source of this extrachromosomal DNA in eukaryotes. The fact that this organelle contains its own DNA supports the hypothesis that
DNA methylation in cancer DNA methylation in cancer DNA methylation in cancer plays a variety of roles, helping to change the healthy regulation of gene expression to a disease pattern. All mammalian cells descended from a fertilized egg (a zygote) share a common DNA sequence (except for new mutations in some lineages). However, during development and formation of different tissues epigenetic factors change. The changes include histone modifications, CpG island methylations and chromatin reorganizations which can cause the stable silencing or activation of particular genes. Once differentiated tissues are formed, CpG island methylation is generally stably inherited from one cell division to the next