DNA system provided the first clear suggestion that DNA carries genetic information. In 1933, while studying virgin sea urchin eggs, Jean Brachet suggested that DNA is found in the cell nucleus and that RNA is present exclusively in the cytoplasm. At the time, "yeast nucleic acid" (RNA) was thought to occur only in plants, while "thymus nucleic acid" (DNA) only in animals. The latter was thought to be a tetramer, with the function of buffering cellular pH. In 1937, William Astbury produced the first X-ray diffraction patterns that showed that DNA had a regular structure. In 1943, Oswald Avery, along with
Single-cell DNA template strand sequencing cells are treated with bromodeoxyuridine (BrdU) which is then incorporated into their nascent DNA, acting as a substitute for thymidine. After at least one replication event has occurred, the daughter cells are synchronized at the G2 phase and individually separated by fluorescence-activated cell sorting (FACS). The cells are directly sorted into lysis buffer and their DNA is extracted. Having been arrested at a specified number of generations (usually one), the inheritance patterns of sister chromatids can be assessed. The following methods concentrate on the DNA sequencing of a single daughter cell’s DNA. At this point the chromosomes are composed of