DNA is the molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and some viruses. It is located in the chromosomes within the nucleus of cells and is transmitted from parents to offspring through the inheritance of chromosomes during sexual reproduction, where the sperm and egg each contribute half of the DNA to create a unique genome in the zygote. DNA determines identity through DNA fingerprinting techniques that analyze variations in repeated DNA sequences at specific locations, known as short tandem repeats, which can be used for forensic identification purposes due to DNA's stable and unique nature.