Extrachromosomal Circular DNA are composed of chromatin and replicate in the nucleus of the cell during cell division. Unlike typical chromosomes, they are composed of circular fragments of DNA, up to only a few million base pairs in size and contain no centromere or telomere. Extrachromosomal Circular DNA Extrachromosomal circular DNA (eccDNA) is circular DNA found in the nuclei of plant and animal cells, including human cells, in addition to chromosomal DNA. eccDNA can be from 200 up to 5 million base pairs in length. eccDNA has been found in the nuclei of human cancer cells and shown to carry many copies of
Single-cell DNA template strand sequencing the ability to acquire sequence information from the Watson and/or Crick chromosomal strands in an individual DNA library, depending on the mode of chromatid segregation; a typical DNA library will always contain DNA from both strands. The authors were specifically interested in showing the utility of strand-seq in detecting sister chromatid exchanges (SCEs) at high-resolution. They successfully identified eight putative SCEs in the murine (mouse) embryonic stem (meS) cell line with resolution up to 23 bp. This methodology has also been shown to hold great utility in discerning patterns of non-random chromatid segregation, especially in stem cell lineages. Furthermore, SCEs