Short answers, pulled from the story.
DNA, or deoxyribonucleic acid, is a polymer of two polynucleotide chains that coil into a double helix. It carries the genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.
The four nucleobases in DNA are cytosine, guanine, adenine and thymine. Adenine pairs only with thymine through two hydrogen bonds, and cytosine pairs only with guanine through three hydrogen bonds.
James Watson and Francis Crick completed the first correct model of the DNA double helix, published in the journal Nature on the 25th of April 1953. Rosalind Franklin and Raymond Gosling's Photo 51 was critical to obtaining the correct structure, and in April 2023 scientists concluded Franklin was an equal player in the discovery.
The Swiss physician Friedrich Miescher first isolated DNA in 1869, finding a microscopic substance in the pus of discarded surgical bandages. Because it resided in the nuclei of cells, he called it nuclein.
DNA profiling, also called DNA fingerprinting, compares the lengths of variable repetitive sections such as short tandem repeats and minisatellites between people. It was developed in 1984 by Sir Alec Jeffreys and first used in forensic science to convict Colin Pitchfork in the 1988 Enderby murders case.
During replication the two DNA strands separate, and an enzyme called DNA polymerase rebuilds each complementary strand through base pairing. Because DNA polymerase can only extend a strand in the five prime to three prime direction, different mechanisms copy the two antiparallel strands.