Barbara McClintock, working in relative isolation at Cold Spring Harbor Laboratory, discovers in the late 1940s, through meticulous study of coloration patterns in maize kernels across generations, that certain segments of genetic material do not stay fixed at one position on the chromosome but can move from one place in the genome to another, activating or deactivating neighboring genes depending on where they insert. McClintock calls these segments "controlling elements" — later universally known as transposons or "jumping genes" — and shows that their movement explains hereditary coloration patterns in maize that did not follow conventional Mendelian rules of fixed inheritance. The finding directly contradicts the dominant view in genetics of the time, which conceived the genome as a stable, ordered sequence of genes in fixed positions, analogous to beads strung on an immutable necklace. Decades after her discovery, transposons would turn out to be ubiquitous in the genomes of bacteria, plants, and animals — including the human genome, where they make up approximately 45% of total DNA — and would become a fundamental tool of modern genetic engineering for inserting genes of interest into laboratory organisms.