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 cellular processes. Briefly, pulse-chase assays allow researchers to track radioactively labelled molecules in the cell. In experiments used to study non-random chromosome assortment, stem cells are labeled or "pulsed" with a nucleotide analog that is incorporated in the replicated DNA strands. This allows the nascent stands to be tracked through many rounds of replication. Unfortunately, this method is found to have poor resolution as it can only be observed at the chromatid level. CO-FISH, or strand-specific fluorescence "in situ" hybridization, facilitates strand-specific targeting of DNA with fluorescently-tagged probes. It exploits the uniform orientation of major satellites relative to the direction