deoxyribonucleic acid, desoxyribonucleic acid, DNA(noun) (biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information.
But even adults don't often know what a notochord is. A notochord is a primitive beginning to the backbone. It appears in embryos as a small flexible rod made from cells from the mesoderm, which is one of the three layers of cells of embryos. Notochords are only found in the phylum chordata, a group of animals that includes humans.
Animals with a notochord (supporting rod of cells along the upper surface). Chordates are regarded as the most highly developed of animals and are subdivided into subphylums called urochordata, cephalochordata (meaning that the notochord is in the tail and head respectively) and vertebrata. Our interest is in the last one which is then divided into five further groupings: