Day 19 of #LMB365 brings a DNA fibre assay from the group of KJ Patel in the PNAC Division. Living cells are treated with two kinds of DNA building block chemicals, which they incorporate into any actively replicating DNA. The DNA from these cells is then spread on glass slides and antibodies are used to label the replication tracts where the chemical building blocks were used for DNA synthesis (shown in green and blue) and the rest of the DNA, including that which wasn’t replicating at the time of treatment (shown in pink). This technique is used to study dynamics of the DNA replication fork, such as in the context of DNA repair defects